i suspect the bbc already have talked to apple about this. there's been a few press reports of mark thompson meeting directly with steve jobs, and i've little doubt it would have been discussed, but i think it's very doubtful the functionality is already built into fairplay. i know there are content providers asking apple for it on itunes and being told that it doesn't exist yet.
but hopefully apple will get on such functionality fairly quickly – it would not surprise me in the slightest if apple sorted it out before the iplayer even launches, and then a mac version could well hit alpha the same time the windows version launches, and all of this will seem something of a fuss about nothing.
ultimately though, it's important to bear in mind the rights situation for television is different to that for music. labels normally own full copyright, whereas broadcasters don't. and given those separate pieces of copyright are sold on to different sources aside from the broadcaster, the bbc is never, ever going to be able to make all it's programmes available indefinately, and therefore needs to have some form of drm solution. of course, bbc worldwide is a different matter, and it's a likely situation that you might be able to pay £2.00 a programme to provide for the residuals and remove the drm from a bbc file after the end of the 13 weeks.
if people are writing, i think their ire to the trust is much better aimed at the rediculous notion of cutting down the 13 week window to 30 days for some nebulous guess that it might harm services that don't even exist with no evidence whatsoever.