a) what about the economic incentives for early users? That is a pretty huge deal too, even if ICO funding wasn't possible.

b) it's not literally useless outside, you just have to exchange it for other coins to use it outside. Isn't that how cash in most countries work too? Besides, remember there's far less friction in exchanging app-specific tokens by another coin than there is in exchanging cash today.

Even if app-specific tokens do not become standard in the future, it's an interesting idea worth exploring. But the whole point is how different kinds of business models can be created due to the decentralized nature of blockchain, this is just one of them.