A lot of the confusion is based on users who haven't actually used it first hand, those who called up to t-mobile and received the incorrect answer from an uninformed employee, or asked a very broad question.
E.G.
"Will I have internet?"
"No, that's only in the BIS/BES plans."
Internal e-mails do not go out saying "Hey guys, this is the specifics on how we make the email only work and where the loop hole is." Some of Tmo's employees are savvier and understand how it works and will say "it's ok, you can still use it for apps", but no where have they received instruction to do so. Would be bad for business if BIS users started to head over in droves because they found out for half the price all they will lose is the BB browser, but still be able to use the TCP and BIS connections for 3rd party apps like Opera Mini, so imo they keep them a bit in the dark for a reason. I always warn when people go outside the realm of what a plan is intended to do, tread lightly. Saying "I didn't know!" rarely gets you out of surprise charges that can happen when carriers catch on to abuse of any particular feature. I personally doubt they're following that closely, but you never know.
Wifi speed depends on a lot of factors, including your particular router setup and connection. The BoyGeniusReport did a direct test between actually had EDGE load faster for data-heavy webpage than WiFi, but some of us on the site did a similar test while loading an mp3 over the browser and WiFi spanked it.