The BBC already does this.
There are at least four or five BBC channels that are only accessible via Sky services or digital subscription. If you don't have access to these services, then you're stuck with the regular channels.
Now you can get an add-on to your regular TV which will allow you to view these services; it's called a Sky Box.
Or indeed freeview. You also neglect to mention that the analogue signal is soon to be turned off, so when that happens if you can get a signal you will get all the channels.
but I really don't see why the BBC should be prevented from continuing to push the boundaries of broadcasting, just to keep less than 1% of the computing population happy.
Because that 1% have already paid for the service. I don't think picking one codec over another could really be labelled as pushing the boundaries, simply putting stuff online is pushing the boundaries more than choosing WMV over XYZ.