Cost - There is no single licensing body, like there is for DVD. A DVD license, includes CDs, VCDs, CD-R, CD-Audio, etc. Right now, Blu-Ray includes... Blu-Ray only, you then have to go out and get rights for every other format that it is compatible with. HD-DVD did not have this problem, as it was simply DVD with HD support.
Actually, Blu-Ray and HD-DVD were virtually identical. They use the same codecs (MPEG2, H.264, VC-1, Dolby True HD, DTS HD-MA, etc.). The differences were only:
- Physical disc format (the drive mechanism required)
- Interactive layer (HD-DVD used soemthing from MS, BD uses Java)
- Blu-Ray added a 2nd layer of encryption on top of what HD-DVD provided.
Don't forget Blu-Ray's inventors, Sony and Philips, were part of the DVD forum and were working on DVD's successor. They split off to do Blu-Ray when the DVD forum wouldn't agree on the tiny differences above. It's a shame, I hate format wars, but Blu Ray won and it's over.
I don't think a DVD license includes older formats; the DVD LA (Licensing Authority) is just a clearing house to license all the patents needed to make a DVD player in one place -- instead of separately going to IBM, Toshiba, Sony, Philips, etc. Even then I think it doesn't include the DTS license, that's separate.
Also I believe the Blu-Ray people have set up a similar licensing authority in the last year.