@eli This is true. But in terms of my personal priorities (YMMV) the ability to silo less important accounts at services that I trust less is more important than the lock-in. Especially given that most, if not all, of the usable alternatives leverage my private data for their profit and have their own systems of lock-in. (Like what Google is doing with Gmail, GDocs, etc.)
At least on Apple's systems you have the option to reach for those anonymised sign-in methods when you need them.