Bearing the above in mind, I bet Canon crippled the AF in the 5D2 specifically to stop everyone buying the 5D2 over the others.
I beg to differ. It is just marketing strategy.
They made such huge advancements in the feature-set and resolution that they could easily get away with keeping the old AF system in tact. This may've also helped with R&D costs early on, but who knows.
What I do know that with the release of 7D, it has become quite clear that Canon is looking to provide a 1.6x crop alternative to those who own EF-S lenses and aren't exactly ready to buy invest in the more expensive, optics optimized for full-frame. The 7D has assured us of a couple things:
A camera body (3D or 5D III) will be released using the same AF brain of the 7D which could easily get away with 9 reliable AF points while making minimal improvements in all other departments and sell like fire during the Ice Age.
This full-frame camera will also have 100% VF coverage not only because the 7D boasts this underrated feature, but in the event that it is the 5D III that sees this AF improvement, it would be accurate to assess it as well from chronological increases (5D = 96%, 5D II = 98%) in given area of topic.
Only time will tell though.