In context, in fact, it's actually a promotion: by treating a MacBook as "just" a device, it finally gets the same quality of sync functionality as its iOS peers. It has been trailing in this respect for a long time -- you couldn't get Mac-to-Mac calendar sync, for example, without shelling out $100/yr. (Yes, there have been workarounds, like going through Google or Yahoo. They've never been very good.)
What's useful about the "demotion" is that it's actually additive: OS X used to be thought of as the server; now, it can act as both a server and a client. Hopefully, this will eventually extend to direct peer-to-peer connections, so that one iTunes library can be synced with another (just as if it were an iPod), or one laptop can play video on another laptop's screen. I'm guardedly optimistic.