Screw this "most people don't bother ganking" claim...in my experience most people will immediately gank you if they have an opportunity (especially if they outnumber you) and will carebear it up if they're at a disadvantage. Depending on the situation, my daily quests can take between 20 minutes and 2 hours solely because of PvP. Extrapolate that over months and it adds up.
All that being said, I don't care if they open up these transfers. Hell, it would make some people happy and Blizzard would make some extra cash, so they probably should. But if they're gonna make a philosophical point about it, I can see where they're coming from.
Right, I didn't say people don't gank. I just said that the scenarios people come up with to justify not allowing transfer are generally exaggerated. i.e. except on the really huge servers, there isn't a bunch of lvl 70s sitting in old world zones ganking all the time anymore, and being at the forefront of the leveling curve now with an expansion, the ganking is pretty low considering the density of the players in the zones. It's just reinforcing your point, people only gank when they have an advantage. If the zone is packed, like hellfire the first week of TBC, everyone carebears up because there's a ton of opposing faction right there too.
I also think a lot of people are underestimating how many people would actually transfer TO PvE servers FROM PvP if they knew they weren't going to be locked on PvE servers forever. Progression is generally slower on PvE servers, and I think one big reason is that your potential recruiting pool is so much smaller since no one wants to make a permanent switch like that.
I don't think all the PvE servers would become ghost towns as everyone goes to PvP. I think low population servers would definitely stay the ghost towns that they already are. But, I doubt any medium-high pop servers would suffer huge hits.