For one thing, primarily, it's hard to have an awesome spot in the draft when you finish in first place pretty much every year. Oh noes the Yankees aren't willing to throw away some years!!! Anyway. In 1991, the Yankees were sixth in the draft. Ahead of them were the Astros, and the Astros had their sights on this skinny kid named Derek Jeter. For whatever reason, though, the Astros decided, at the last minute, not to sign Jeter; they signed Phil Nevin instead, which meant the Yankees got Jeter. Luck.
IIRC, Mariano Rivera wasn't considered a real gem at all. His cousin, Ruben, was the guy the Yankees were really after. Well, Ruben's legacy pretty much consists of stealing Jeter's glove and getting kicked off the Yankees for it, and this, whereas his cousin is a not-half-bad pitcher. Luck.
Andy Pettitte was supposed to be in the bullpen until he was forced into a starting role in 1995 because the Yankees didn't have enough starting pitchers. Turns out he was pretty darn decent there, who knew. Luck.
The Red Sox signed David Ortiz for peanuts because he wasn't really great with the Twins and there were no indications he was going to become the incredibly scary hitter he was in 2003-2007.
Prior to 2004, both the Yankees and Red Sox wanted Javier Vazquez as he was a young pitching stud (you know, what Verducci slams the Yankees for not having throughout the entire book). The Yankees got him. Then, they both wanted Curt Schilling, who was an older pitcher but one with a pretty damn good track record of success. Schilling actually wanted to go to the Yankees (ugh). The Diamondbacks were still very bitter from the fact that Wells had gone to the Yankees after he had supposedly agreed to go to the Diamondbacks, so, out of spite, they asked for the moon and stars from the Yankees, who didn't want to get rid of some of their better minor league pieces. On the other hand, they asked for crap from the Red Sox, who happily gave them what they wanted. Luck. (This still actually worked out for the Yankees because, if we got Schilling, we probably would have never gotten A-Rod.) Verducci makes a big deal out of the AL/NL thing to say how dumb the Yankees were for getting Vazquez. It's a fair point, but the last time Schilling had pitched in the AL before 2004 was 1990; he'd appeared in a total of 44 games, pitched 69.1 innings, and started only 5 games. He had an ERA of 4.54 for an ERA+ of 85. The fact that he was so ZOMG TOUGH AND HE HAD A GREAT ATTITUDE ABOUT THE WHOLE THING doesn't really have to do with anything, Tom. I could have the best attitude in the entire world about baseball, and I'm not going to be able to hit Roy Halladay.
After the 2004 debacle, it was pretty obvious the Yankees needed pitching and badly. They panic-traded away Vazquez, then, like most people, turned to the best pitcher available on the free agent market, Carl Pavano. Most of the competitive teams, the Red Sox included, were going after him, but Pavano went to the Yankees for less money because he really wanted to be a Yankee. Luck.
As for the Hanley Ramirez trade, hmmm. I think it was a pretty good trade for the Red Sox, because Beckett really helped to bring them a World Series in 2007. But you could make the argument that it wasn't all that great because the Red Sox obviously had an issue in 2008 and 2009 with both offense and the shortstop position. Hanley's probably the best shortstop in the game right now, plus he affects the game every day, not just every five days like Beckett. IIRC this wasn't Theo's decision, but whatever.
And so far, after falling all over themselves to praise Theo for his "smart" signings prior to the 2009 season, some suggesting that the Red Sox had a better offseason than the Yankees (lol), nobody in the media has called him out after how incredibly shitty they turned out to be. If Cashman did that, you know that would be the reaction.
Finally, the playoffs, which most use - not unfairly - to determine the best team, are among the biggest result of luck ever. It's not surprising when really really really good teams win, like the 2009 Yankees, but it's also not surprising when lesser teams win, like the 2006 Cardinals. Look at the poor 1990-2005 Atlanta Braves. All that awesomeness and only one World Series ring? The 1996 Yankees should have simply been happy to be there in that World Series. The 2000 Yankees were not nearly as good as the 1998 and 1999 versions. Those guys both got lucky. Some others didn't... (the 2001 and 2003 Yankees were better than the teams who beat them, IMO.)
In The Yankee Years, Torre talks about Mariano Rivera throwing over to 1B a lot before Dave Roberts stole second in Game 4 of the 2004 ALCS, and pretty much blames Mo for warming up Roberts. Torre then claims that he/everyone knew Roberts was going to steal (and yeah, everyone did). Why didn't you call for a pitchout then, idiot?! Posada's throw almost got him anyway and it wasn't a pitchout. It almost certainly would have gotten him with a pitchout. If they get Roberts, Mo probably shuts the door without anyone scoring, and woooo the Yankees are on to the World Series. In a regular season game against a really good pitcher, it's generally not a horrible thing if your best hitter goes 0-4 because the next day, you're probably gonna face a pitcher that's not as good. That doesn't really happen in the playoffs and having two bad games in a best-of-seven and especially best-of-five series can put your team in a pretty big hole.
The 2004 Yankees weren't better than the 2004 Red Sox, but they experienced some pretty bad luck. So did the 2005 Yankees (I don't think there's any way they would have beaten the White Sox if they got to the ALCS, but eh). The entire offense had a pretty shitty three games against a Tigers pitching staff that caught fire in 2006. In the regular season, three bad games against great pitching isn't that big a deal. In the postseason? It's huge. A freak cloud of bugs that rattled a barely 22-year-old right out of the minors pretty much doomed the Yankees in 2007. If luck goes the Yankees' way in any of those years, are the Yankees still essentially failures who did everything wrong as opposed to the teams of the late 90s and early 00s, who did everything right and were truly united or whatever BS?