One thing I noticed when looking at the standings is that Houston has done much worse that you would have expected considering its runs scored and runs allowed. Bill James found that RS/RA is a very good indicator of a team's W/L record. Look at the standings at the bottom of this page; most teams are within 3 games of their expected record. James's Pythagorean theorem: Runs scored [squared] / (Runs scored [squared] + runs allowed [squared]).
W L GB RS RA EXPTD DIFFFrom looking at those RS/RA, you would expect the Astros to have a 9-game lead over the Cubs. One reason for this could be a large number of blowouts, though those do tend to even out over 162 games. Looking at Houston's schedule, they've actually won many more blowouts than they've lost. By my count, in games decided by 8 or more runs, Houston is 12-3. I could say it's Jimy Williams's fault, because he managed in Boston before going to Houston and I know all too well his horrid lineup construction and (over)use of the bullpen (... must ... suppress ... rage ...), but it may not be that easy.
Cubs 88 73 -- 716 678 85 76 +3
Astros 86 75 2 797 672 94 67 -8
First, Jimy's Pythags in Boston were within 1 or 2 games every season. Second, it's partly due to Jimy's strategies that the Astros have scored and allowed the amount of runs they have this year, so compare that to what they should have done under Jimy is almost like comparing an object to itself. ... Regardless, I still think Jimy is a horrible manager and the difference in the little chart above remains fascinating.