It only makes sense. They're both effectively the same OS, just different UI veneers. And Apple customers are eating up apps on the platform and most don't seem to be bothered by the lack of choice/competition thing; Steve would have been remiss not to at least try the waters with the iPad, and look how well it's selling. I'm one of those guys who would only even consider buying the thing only if it had actually shipped with OS X proper, but clearly I'm in the minority.
I own a couple older iPod Touches and a 2nd generation Mac Mini -- which is pretty much nothing but an HTPC that allows for some light surfing/VNC while my kid watches a cartoon or two for the hundredth time.
Disclosure: The Mac Mini replaced a really sweet 1GHz EPIA-based Freevo box that I had custom built both the hardware and software for; it was bliss. Totally diskless operation with netboot, very low power consumption, and ran everything from DirectFB so X wasn't even required. It was however quickly replaced as soon as I bought an HDTV as it could barely play h264 video at DVD resolution, and the motherboard didn't even have a DVI port. I might have done it again for a replacement, but I spent many long days setting the thing up -- The Mac Mini on the other hand came out of the box, got put on the stand, some cables plugged into it, and I was done.
Once upon a time I might have thought, "You know what, that's fine, let them do that, I'll just keep running my old OS and not upgrade" -- but I'm sure I'm not alone in realizing this isn't really an option at all anymore; no more bug fixes, security patches, and third-party software support disappears shortly thereafter (problematic for a media player). There is also the seemingly greater likelihood that the Mac Mini will die sooner than later as the design appears to favour quiet vs. cool operation, which probably isn't an unrealistic expectation based on their target audience.
Long story short, though -- if Apple wants to do this, let them. Given their recent business activities I've already decided to put a moratorium on buying any more Apple products, which is fine as I've always been a white-box guy anyway. I will admittedly miss running Plex as it is a beautiful media player, but I would rather have the freedom of choice than spend that much on hardware and have a vendor decide what's best for me to be allowed to run.