Well, the reason I asked is that as far as I know, a lock screen and password requirment is not on by default in the Trophy or any other version of WP7.
However it is common practice (and a good one IMHO) for system administrators to place a password/pin policy on any device that accesses their email system. This is almost certainly why you got the requirement to set a password as the first time your email attempted to sync your email account the policy would have kicked in.
The policy is semi-permanent in nature. Once the policy is pushed to a phone, you would generally need to do a hard-reset to wipe the policy.