Racketear,
A lot of times, software will list arbitrary system requirements, but in theory you it would "run" under a 386 w/ Windows 95 and 8 MB RAM.
Sometimes, the requirements are important, as the publisher doesn't want a user running a game on a machine that's too darn old, for example.
Other times, the opposite effect happens. To try and attract as many customers as possible, the system reqs might be P166/16 RAM. The app will run, but it runs like a dog. It all depends on the software.
As far as KNI (isn't this the SSE instructions?), unless I'm wrong, the earliest P3's didn't have these new instructions. And the K6-2 never had them at all.
In this case, I think the listed requirements are more to target the computers that could benefit from the product, than incompatibility.
Most people who slapped a GF2 MX card into their Pentium systems (assuming it works) would find little performance benefit, and then think that the product is either defective or lousy.