I changed my gmail password a day ago, but my phone does not require me to put in the new one. I can still access my gmail with the old password. Why?
Phone is rooted, sim unlocked , running android 2.3
Your phone doesn't store the password, it has some kind of session key. I would have expected it to be invalidated when you changed the password, but apparently Google doesn't do that. You'd have to ask them why.
Are you sure that you are not seeing locally cached data? I just tried it my self and changed my Google password. Directly afterwards the GMail app wasn't able to send or receive any mails on my Desire with 2.3 custom ROM.
Warning to everybody who want to verify this on his own: If you try this on your own remember that you can not change your password back to the original one. Google saves it and you can never use it again!