I just got my commuter for my 4S today and I've also noticed the lock button to be a bit difficult.
Whenever I had this problem on the commuter for my 4 it was usually remedied by taking the case apart and reseating it.. I've already done that once, but I'll try it a few more times before I say it's an issue with the case.
Also, I don't like how the headphone jack cover and 30-pin cover are just that, covers. On the version for the 4 they actually had rubber that inserted into the respective holes. I felt that offers more protection from like dust and would be more likely to keep liquids out if on the off chance the phone got wet (which my 4 did when I accidentally dropped it outside a tent where it sat in the rain for half an hour 😱 and it was perfectly fine. The little color changing liquid tabs didn't even change)