I'll throw my 10 cents in here, iam an old player as some people know =) i've been playing fighting games since i was maybe 2 years old? way before some of them even existed.
I was a street fighter champion, specially hyper fighting, street fighter was a game where you really needed execution and time your moves precisely, now you can buffer moves and skip directions to do everything, even on wakeup moves can be buffered and its a guess if you should block that DP or just bait it.
Mortal kombat requires way more skills and and fundamentals per say, due that just holding the block button when it matters you will avoid being hit or comboed, on street fighter or any other game blocking back, you can be walking back freely and not worried about fast advancing moves, this makes footsies a litle braindead since the computer will block automatically when it requires to block, also you can block and tap normals for when the computer gets you out of blockstunt attacks will hit your opponents without you worrying releasing back blocking =/, also on SF4 knocdowns become a guessing game, even out of throws you have enough time to get your opponents to guess your jumps, safe jumps, cross ups, safe jumps sweep, jumps can be so tricky and mindfucking, on mk you dont have these kind of craps, also AE has a guaranteed ultra move per round while you getting hit, come back factor is ridiculous cause of guess and free ultras, a lot of top players lose on this game cause of the guessing factor not for really being outplayed. there is so much more i could add but its too much really and don't wanna go over it all.
MK players do really have more fundamentals or at least the game requires you to.
