Have you tried IM+ ? That was how I was able to get Skype on my Palm Pre, but it was not an always live connection and was more of a pain to use. Hopefully their BB App is better, though I haven't tried it out yet.
Yup. Skype signed an exclusivity deal with Verizon.
Plus, Skype on BB isn't true VOIP. It calls into Verizon's network, then communicates digitally. So the software is set up to use Verizon's cellular network (instead of wifi), which is why they have the exclusivity agreement.