CPUs "learning" isn't really the case at all. From my experience, they just adapt to your playstyle and the process, they may use some of your combos and ATs. From what I've seen, CPUs act a lot like humans: If we see a player spamming a move, won't we try to get past it or just fight fire with fire? If you were to go up against a MK spamming his Nado, would you try to find some way around it or would you just spam your own Nado to get that MK to stop? What we do isn't really much different than what the CPUs do.
Here's somethng fun to do: Have a ditto match level 9 CPU and choose only one move use against that CPu and don't stop using it, chances are that the CPU will start using that move. An easy thing to do is wavedashin-...er, SHing aerials for a while. Eventually, the CPU will catch on and start SHing the exact same aerial. Now, if you were to SH that aerial into a combo several times, the CPU would (imo) make an attempt to try that combo only to fail at it (though, CPUs have no fear of messing up and will make you think that they planned a follow up for a failed combo).