Thanks for your comment. I certainly agree with your points #1 and #2. However, the opportunity to capture 30% of Adobe's, Microsoft's, Avid's, and others' Mac revenue constitutes a large, not a little, gain.
Just looking at Adobe, it's likely that Apple could make $300 million a year if they could tax all Adobe's Mac sales (admittedly, that wouldn't happen for quite some time). That's a significant chunk of the $1.7 billion Apple is currently on track to make off of App sales in a year, and that's just from taxing one company.
Also, Macs are still a profitable market that's not going away anytime soon. Apple may be making way more money off of iOS than OS X, but they still enjoy great margins and profits from the Macs. Apple's calculation will be that they can make OS X even more profitable if they make it more like iOS.
Finally, the other pieces of the ecosystem, such as roaming user accounts between Macs and iOS devices, are big features that they want to implement. Apple has already forced Mac App Store applications to be sandboxed, while also restricting certain APIs to App Store-distributed applications. They're already on the road to Mac lock-down, it's just a question of how fast they'll get there.