You also have to balance a top regular season team v a top playoff team.
A playoff team needs three things
1) players who aren't "homers," that is, are as comfortable playing on the road
2) top 3 starters who can compete in big games (4th will get a couple starts in the playoffs, 5th none at all)
3) a solid bullpen 1-6
Now in the regular season, 4th, 5th and 6th starters matter more, but it's worth giving up regular season wins to keep your top 3 rested, same with the back of the bullpen, you may lose some games pitching inferior middle inning guys to rest your top guys.
So to me, once you get past 90 wins or so, setting yourself up for a playoff run is more important than a few more wins unless you have a team full of homers or a home field advantage (Colorado, for example, maybe Fenway).