The Cubs are the best team in the NL, but the gap is not that big.
Offensively, Chicago led the NL in runs this year by a wide margin, but that overstates the case in their favor. The Cubs were projected to score fewer runs than both the Phillies and Brewers this year. That matters, because teams regress
As for pitching, it's easy to forget that the Cubs' Game 1 starter had ERAs of 4.80 and 4.72 as a one-inning reliever the past two years, or that Carlos Zambrano now has the peripherals of a 4.60 ERA pitcher. Fortunately for the Cubs, they have maybe the best starting pitcher in baseball right now...and they're relegating him to one start in the NLDS, because they're idiots. Simply naming Harden the Game 1 starter would improve Chicago's chances of winning the World Series by a full percentage point, but that would be too easy for Lou Piniella.
Looking at the BP Adjusted Standings, we see that the Cubs are a 95-win team playing against three teams in the 87-89 range, all of whom are managing their rotations better. That adds up to much less than a 40% chance to advance to the World Series.
The Angels are certainly not the best team in the AL. You won't find any metric besides W-L record that puts them ahead of the Red Sox or Rays. In fact, they're not just worse than those two teams, they're worse across the board, unable to match either team in offense, defense, or pitching.
Anaheim had the run differential of an 88-win team this year, and the peripherals of an 84-win team. You can argue until you're blue in the face about their "ability" to win close games, but the truth is that this was a fluke season; the Angels may have been the luckiest team in MLB history.
How can a team be built to win a disproportionate number of close games? A strong bullpen? The Blue Jays had a 2.94 relief ERA this year (wow) and they went 24-32 in one-run games. The Dodgers, third in bullpen ERA, went 19-24. Meanwhile, the Rangers--who had MLB's worst bullpen ERA and a losing record to boot--were a robust 28-18 in one-run contests. San Francisco's pen may have been the worst in the majors after park adjustments; they went 31-21 in one-run games, and 41-69 in all others.
What about batters delivering timely hits? The Twins were by far the best clutch hitting team in the league this year: they batted .280 overall, but a whopping .306 with runners in scoring position, which is the only reason they're still in this thing. That plus Joe Nathan's 1.34 ERA led to a 26-25 record in one-run games.
This "ability" is a backward-looking measure, like clutch hitting. It's easy to name last year's best clutch hitters, but nobody can identify next year's. Similarly, you can tell which teams have overperformed this year, but not who will do it in the future--and the future includes the playoffs.
The Diamondbacks were 2007's poster children for overperformance after going 90-72 with a -20 run differential. This year, they improved that differential to +14, yet fell to 82-80--right in line with expectations. The carryover is a mirage.
That's basically it--the Angels are clearly the third-best team in this field, and their odds reflect it. Their chances would be even worse if they didn't have home field advantage and only one game against Josh Beckett.