the 7D is the successor to the 50D. Everything on the 7D has been improved upon from previous bodies. 50D had 50% more MP than the 40D, shot faster, higher ISO, the 40D had more MP than the 30D, shot faster, better ISO, more features.
The 50D is 2 years old. I think that fierce competition has forced Canon to decrease their usual 18month product life cycles (prosumer-semi pro lines) to about 12 months. The 7D simply has improved upon the xD line. The AF improvement was sorely needed.
I think what they need to do is move the xD line to a 1.3x crop (alongside the 1D), leave the Rebel line at 1.6x, and then you have the 5D/1Ds line at FF.
Don't worry, the 1D have the advantages, such as better AF, larger buffer, dual card types, faster frame rate, etc.
I wouldn't mind a stripped down 5D2 model. Not everyone needs video. If they made a 5D2n, (everything but video) and shaved the price by $500, i'm there.