I think Combo discs can be good and can benefit HD DVD owners. Its just not going to benefit most current owners who can't bear to watch DVD's even again after watching HD
There's 2 benefits to existing and future HD DVD owners.
1) Rentals. I've rented a few times and then gone to Cape Cod for the weekend and was able to bring a few rentals with us since they were Combo's.
2) Portable or other DVD players in the home. The typical consumer who hasn't invested in HD DVD's yet very likely has a portable player, car player and players in various rooms. They may have one of the above or all of them. They are not going to replace all these at once and when these consumers are ready to invest, this can be a big benefit to them
The problem however is at what cost does it become a true benefit? Let's look at 300.
(Prices in MSRP)
300 DVD is: $28.98
300 HD DVD (not combo) would likely be: $34.99
300 HD DVD Combo is: $39.99
So, is a DVD owner willing to pay $10 more? Unlikely. Would they pay $6 more? I'd still say unlikely. I think $3-4 tops would possible be worthwhile.
And I think most HD DVD owners (given a choice) might pay $2 more or so in some cases.
So the big problem I see with the Combo's is their pricing. They need to structure it in a way where it is viable for both DVD owners and HD DVD owners.