The DVD consortium requires a fee to get access to the decryption keys necessary to play a copy-protected DVD. The fee is 'per device' so you have to pony up for each physical DVD player (no big deal) or each piece of DVD player software you distribute (potentially big deal).
Since no one (to my knowledge) wants to pay $$ a pop to distribute a free software DVD player, and no company thinks they can make a profit selling one to Linux users, the only alternatives are free players that use the DeCSS code to break the copy protection.
The same will be true for Blu-Ray and HD-DVD, except that presumably their copy protection is much better than the pathetic stuff that was used for standard DVD, making (free) Linux players less likely.
On the one hand, it's kinda stupid at this point to insist on the fee, since the cat is pretty much out of the bag. OTOH, given how a large segment of the Linux community can be such jerks about god-forbid actually paying a few bucks for a program, I can see why no commercial vendors have bothered.