Accepted Penalties by Week, 2007 NFL Season

We crunched the numbers for the number of accepted penalties per game by week during the 2007 season. This doesn't cover other seasons so it is just a limited look. We expected to see lots of penalties the first few weeks (while the players got used to rule changes or worked out the pre-season sloppiness), but that doesn't seem to be the case.

The first 7 weeks were roughly around 11.6 per game, then it increased in weeks 8-10, then more or less settled to a level slightly lower than the first 7 weeks for the remainder of the season. Any thoughts?

Weeks 1-7: 11.56 accepted penalties per game (ranging from 11.25 to 12.07)
Weeks 8-10: 13.29 per game (from 13.08 to 13.43)
Weeks 11-17: 10.69 per game (from 9.56 to 12.25)
1: 11.25
2: 11.75
3: 11.38
4: 12.07
5: 11.36
6: 11.62
7: 11.50
8: 13.08
9: 13.36
10: 13.43
11: 11.25
12: 10.06
13: 12.25
14: 10.50
15: 9.56
16: 10.00
17: 11.19