Here's a quick look at the breakdown of Grounding into Double Plays by batting order spot and by league.
The plot shows the fraction of total GIDPs committed by each spot in the batting order. This is for 2011. Don't pay too much attention to the specific bobs up and down--for example that in the NL, cleanup hitters grounded into a lower percentage of DPs than the #3 and #5...it varies a bit from year to year.
The key things to notice are that the #9 AL hitters ground into more DPs than the #9 NL hitters--presumably because the #9 NL hitters bunt a lot more often, which cuts down the odds of a GIDP. The NL #1 hitters also GIDP less than the #1 AL hitters, presumably because they have fewer guys on first base since it's usually the pitcher hitting ahead of them.
The result is that, generally speaking, the #2 through #8 NL hitters are higher than the corresponding order position in the AL.