Clearly legal, because you're a lawyer? Don't be too surprised if this lands Apple in court eventually. Leveraging their OS to disrupt competitors in other business markets is the exact sort of behavior that got Microsoft in trouble with Netscape.
AFAIK, this behaviour is only illegal if you're deemed a monopoly. Certainly Apple doesn't have a monopoly on smart phones, but it could be argued that they have a monopoly on app store purchases, since I'm sure that they have a greater than 70% share (by dollars) of app store purchases.
Naw, there is stuff that can land them in court for restrant of trade issues.
I hope this motivates amazon to support the jailbreaking community and release a new amazon store, but really how this will pan out is apple will get like 5% of amazon sales on top of the fees for CC processing.
But also clearly not in my interest as a putative Apple customer. (Alas, I fear I am not in Apple's target market.)