The Beeb don't have to make it run on ANY platform & they'll still be charging you a license fee if you watch television.
Truth is, they've delivered a proof of concept Beta version that runs on a platform with a wide enough userbase to give it a decent test.
Sounds pretty sensible to me.
As for Linux - in the UK, the Beeb broadcast their program's in English. That's because the most common language in the UK, is (surprisingly) English.
The broadest reach for the least development cost. Sensing a pattern yet?