I know. The only real functioning properly multi GPU cards came from 3dfx.
ATi did dirty tricks as well, really?
The only thing I know is, that not long ago some German hardware magazines adjudged the new ATI cards as worse than Nvidia cards, because they had "Problems with their testing Hardware" (how it was called on their website, later).
In the magazines itself I've never red about this concession.
Ironically the same magazine sells Nvidia graphic cards under their name...
Also in the PCAction some time ago, ATI cards had harder test parcours, and caused by that lower frame rates; only mentioned by a "*" and explained in a hidden small print...
Maybe you reject this just as a conspiracy theory by me.
In fact I don't like Nvidia anymore, not because of their cards but through their "company policy".
Nevertheless I've got more than 20 Nvidia cards, but only older ones.
Probably the only company without a skeleton in its closet is S3.