The entertainment industry has demonstrated with CD and DVD that they are more than happy to absorb the cost savings from cheaper discs - the price of manufacturing drops markedly but the discs stay more or less the same retail price.
It has always been my belief that if there is any costs saving, the only people that will benefit is the studio - the chance of them passing such saving on to the consumer is next to zero... until of course they aren't selling any and they go to the bargain basement bins...
And yes a $2 difference in disc cost could easily be smoothed over in the early days I am sure...
I will be buying an HD-DVD title to go in my collection next to my DCC tape and my Divx copy of The X-Files movie
Cheers!