they would hit an early-adopter demographic just at the time they were forming many new social connections (freshers) that they wouldn't want to lose by moving to a different network later, and the network effect would make it grow. That ain't no accident!
Theory #1 is compatible with the idea that while what you're saying is true, neither Zuck nor anybody else involved had an explicit understanding of this while they were building it.
Newsflash -- they're all abusive platforms. That's what tech giants do.... And it's not conspiracy -- it's explicit. The VCs that fund them in the start always ask the question "How are you going to protect your market?" -- or in other words "How can we achieve lock-in?"
The problem with this response is that most of the deficiencies I'm describing don't help them do any of this. Apple's abuses related to iOS and its developers are ridiculous on any number of levels but all more or less make some kind sense from a standpoint of QC, promoting future purchases, and lock-in. And, OK, banning AdSense fits in with the goals your describing.
But seriously, what good does it do Facebook if their APIs and SDKs suck? If their documentation is terrible? If they deprecate useful interaction hooks in favor of less useful ones which end up banished entirely? There's really only one advantage -- they push the development costs of polishing these things off their own plate and onto the backs of their third party devs. And they can get away with it because of their position in the market... but that's the kind of advantage that really should only appeal to a shoestring operation with limited resources, not a rapidly growing company with ambitions of having deep ties to many of the future services deployed on the web. It isn't going to help them capture anything.