Well the project I can tested out a bit more (as you call it.)
It appears they have some new adaptive AI type of difficulty that kicks in at a different pace depending on what difficulty you start with. If you play in difficulty one or two it doesn't do it. If you do it on easy(3 of 8) only Seth will use it on you after the first round and it makes it super obvious considering the smack he lays down in comparison to the first round.
If you play on 4/8 (medium-default) 1/2 way up the ladder (fight 4 of 8) the adaptive AI kicks in immediately in round one. Round one will be a bit easier than the second as it will be learning your tactics, but if you spam one too much even in that round it'll whoop your ass, and in round two (and three) it gets just nasty. As it stands I can't get without dying beyond round 4 or 5 on Medium, but I can nail the game on Easy (3/8.) I know I'm not out of practice as I still mess with the old SF2 tree of titles, and in all fairness SF4 feels much like SF2Hyper Turbo Whatever that was remixed on PS3/360. It has that more tight fighting style, the charge up bar, and the rest...but once the adaptive ai kicks in, it's more like a beat down you'd expect from like the old days of MK3 or Killer Instinct where it's 'normal(fair)' and then goes cheapass 3 fights into it where it goes like thug on LSD on your ass.