I don't really see the difference between Facebook leveraging their social network platform to strong arm users into using a Facebook store and Apple leveraging their hardware platform to strong arm users into using the Apple app store. Both of them are bad for users.

I think the way things would shake out is that most app developers would want to have their app in as many stores as possible. Combine that with stores competing to have the largest app selection and you have a much healthier market. Having app stores compete for developers and users would be amazing for everyone except the current app store owners.

I don't think we should avoid demanding a better market for developers and users just because there are a couple of companies like Facebook that might try to abuse their market position to popularize their own app store.