Yup that's all very good, but there's a distinct difference between certain ATI X series cards, nVidia 6 series cards and their lower counterparts. Shader v3 is the most obvious.
Why do you assume that when Mark says he was just guestimating, he's not referring to precisely this remark about ATI X and nVidia 6 series? I can't find anything else that he could have been "guestimating about" apart from that precise remark.
If the only cards on the market that have a decent shader instruction count are SM3 cards, then that kind of means SM3 is going to be a requirement. Right?
It's exactly this kind of flawed logic that Mark criticizes in that thread. Firstly, he says it's just a guestimate, not a specific requirement. Secondly, it's a flawed premise because the only cards on the market that have a decent shader instruction count are NOT SM3 cards. Far Cry is a pretty shader-heavy game ( engine ) and I'm not aware of a single SM3-only effect in the game. In fact, a surprising amount of the effects in Far Cry are possible with SM 1.4 and the rest are 2.0.