You should test things before you make claims like that. I own both an ATI 1950 and lots of NVIDIA cards. I gave up on NVIDIA due to the increasingly buggy drivers.
The ATI card has no spell-lock at all. I can't verify other cards, but from what I've read in other forums (particularly windower forum), many other people have noticed this difference, too. Those posters here with ATI cards that say they have spell-lock are really the only believable ones -- the rest of you just sound like you own Nvidia stock. If you're seeing spell-lock with ATI, perhaps it's a result of directX version AND driver or maybe it's only the recent ATI cards & drivers that don't have the bug.