The differences in passcode lock options are due to whether you are using Microsoft Exchange.
http://support.apple.com/kb/HT3860
See this thread:
https://forums.macrumors.com/showthread.php?p=8454974#post8454974
I had the same change after 3.1 - 1 hour down to 15 minutes. a coworker's with exchange also, did not change. he still is allowed 1 hour. our IT made no change with the 3.1 update. so seems to be an issue with the update. why would one phone do it and not the other?