[ckuhl]

Companies could absolutely disallow / block it.

However they most likely won't for the same reason that people who are upset about Apple's 30% App Store cut still develop apps for iOS: they have their customers spend far more on average than other phone / OS users.

[tinus_hn]

So a company would put a sign in with Apple button in their app, but disallow you from using it?

[WAHa_06x36]

Won't pass review.