Well you see the T-bred's original blood just wasn't conducive to competetive cloning, so they re-engineered some of the genes.
Seriously, what do you think is different? It's a core revision, and as one would expect, B is better than A. Technically, the only real difference is adding an extra layer to the core so that they could reduce signal noise in the core, making it much more scalable than the A.
It's what AMD gets for rushing their .13 micron conversion before it's ready instead of just fixing the problems first and <i>then</i> going to market.
PC Repair-Vol 1:Getting To Know Your PC.
PC Repair-Vol 2:Troubleshooting Your PC.
PC Repair-Vol 3:Having Trouble Troubleshooting Your PC?
PC Repair-Vol 4:Having Trouble Shooting Your PC?