It's not yet clear to me what this "Wifi only" issue is, or whether it's specific to only certain people/carriers/situations. I can tell you that I use my own BB10 device (A Z10, running a very old software release) over WiFi, without problems like the ones described here.
The "forgetting password" issue seems to be a bug, in fact it was a bug even on the older Playbook devices. That has nothing to do with the way the email is retrieved, it is just a software flaw. I do not know why it has persisted so long.
More info on your email account settings would help zero in on what kind of service you have. There are all sorts of potential explanations, depending on your circumstances and how your email provider is connected.
I suggest you take a look at the following for some background:
http://forums.crackberry.com/blackbe...yncing-777774/ http://forums.crackberry.com/blackbe...de-bis-786880/ http://forums.crackberry.com/blackbe...rsions-779341/