I can give a few points for the iOSification people out there.
1. Yosemite requires signed drivers. A bit more iOS like as you can't easily swap in hacked drivers for non-supported but basically the same hardware.
2. Such as 3rd party SSD disks which (afaik all Yosemite betas) do not have TRIM support in the official drivers. This makes people feel like Apple is discouraging self upgrading. Buy a more expensive OEM SSD, or just get a new Mac when you need a larger one?
3. RAM being soldered on more systems such as the new mini.
4. Built in video mode checks preventing retina scaling on 3rd party monitors and the driver signing limitations preventing workarounds.
There's a lot of people who have long feared Apple locking down hardware and making them more appliance like. It's looking like these fears are gradually becoming more realistic. With signed drivers in Yosemite, security has been improved but with another loss of freedom and apparently arbitrary hardware limitations. It's true the OSes at this point are quite distinct, the locking down trend can be easily argued however.