OK, I am not saying you can't play HD data on current equipment.
What you can't do, on stuff currently in the shops, is play data that has been copy protected.
I have a Sony HD camcorder (the "cheap" £1000 one) and it makes great HD movies. The quality (ignoring my cr*p movie making skills) is stunning, and the stuff plays back on anything that will handle 1080i data; typically this means WinXP and the latest Media Player.
Similarly, the fantastic quality shop demo material which is being played continuously, using those specially built DVD players they have in the shops for driving their HD screens, is unprotected.
But copy protected movies? No way. Only possible via the analog input.
It's worth doing a google on HD security. It's pretty amazing what they are doing.
Yes it will be cracked. Probably not as quickly as CSS was cracked. However, this won't be relevant to Joe Public and the [in]capability of the £1500 HD screen he has bought from Comet to show anything in native HD other than Sky broadcasts.
I am puzzled though about e.g. Sony. They make a huge marketing case of their laptops playing movie DVDs. I can't believe that they will go away from this capability with HD movies. Perhaps only future models, with the appropriate decryption in the video subsystem, will play HD movies. Can't see how it's going to work otherwise, because if you can get access to the unencrypted digital RGB data at any point, the whole system will fall over because you will be able to make an exact digital copy of the movie.