They weren't trying to steal IBM's design, they already had one of their own, what they wanted to know was "is there any as yet unannounced functionality in the IBM VGA chip?" they didn't want to be caught out when some unknown registers popped up. Of course it turned out there was as yet unannounced functionality - but not by IBM's design, more because of the orthogonality of the design - MODE-X was discovered and became the basis for DOOM's speed, anyone who didn't support it lost out