They should say so, but it wouldn't look good for Palm to come out and say "Yea, our OS is really old and doesn't support multitasking, which is why it doesn't support UMTS and HSDPA or wifi". Generally, most companies aren't going to come out and say something that would potentially turn customers away or make them look bad, especially if they have some other less shameful excuse they can give you.
I don't remember who exactly it was, but in one of the pre-700p vids, a higher up Palm person was interviewed about the 700p. He said the 700p didn't need wifi because it had Ev-DO and wifi would eat the battery too quickly. He didn't (and probably wouldn't ever) tell you that PalmOS can't handle wifi on a Treo.