The thing that boils my britches about this is that Apple DOESN'T have a competing service. When the services leave, the iPhone is left only with iBooks and iTunes, both of which are expensive and not very good.
I think this will only be bad for users, but not bad enough to force masses of people to leave. There will always be a cost to leaving Apple behind (both psychological and monetary), and if Apple had to invent their own services to replace those that left, I think they would be more expensive and maybe not quite as good as other products, but they wouldn't be so bad as to force people to leave their iphone, which still has many fun/useful features that don't have subscriptions.
I think the only businesses that are in danger of leaving the apple system would be: Music streaming, video streaming, and books, and I think Apple would be able to provide their own in house replacements for those that left (for better or for worse).
Apple currently has to allow these competing services to be made available through their platform, either to make the platform more appealing to end consumers or because of worries of anti-monopolistic concerns or because Apple isn't comfortable with denying these.
I agree that both iTunes and iBooks are rather horrible products, though.