I've seen some 3D stuff in flash, but only simple polygon models. I've no idea how it's done though -
You only think you saw real 3D. :black:
There is no Z axis to animate in Flash, so there is no real 3D.
Things that appear to be 3D in Flash are actually nothing more than 2D images. They are all drawn and then animated frame-by-frame-by-frame-by-frame, etc... add in some tweens, scale shifts, shape morphings, and some tricky (and time-consuming) ActionScripting techniques and the end result appears as if it is 3D.
This is why the things you have seen are very simple polygonal models. To make anything more complex...well, the time it would take to not only draw, but animate as well would take immense patience and dedication, not to mention a ton of time. :black:
This is why there are actual 3D modeling applications out there.