Don't forget Alpha that many times the bluray /dvd/dd combo is cheaper than the stand alone dvd option
Sometimes its just $5 or so more.
Alice in wonderland came out last week and was $22 on bluray. Disney had a $10 coupon for it so it was just $12 and it came with a dvd and DD the last time it was released on dvd was last year and it was from an older clean up of the film.
The first week of next month they are releasing bambi on bluray with the same coupon . Bestbuy will have it for $22 while the dvd is $18 . With the coupon that only works on bluray its cheaper than the dvd and comes with the dvd and bluray.
Its not hard to see why people will choose the bluray over the dvd version. Even if you discount the bluray as an extra for many who have dvd players and pcs or portable devices the DD makes a very valid add in as it can be viewed on many devices. So for those even without bluray discs the $5 or $8 more over the dvd edition it would still be worth more for some than the dvd.
They are adding in value to the bluray disc because the bluray verison wont sell as well without it.
In the case of AVATAR the Blu-Ray + DVD combo was not cheaper than the standalone DVD. And it did not have a DD option.
Blu-Ray is a successful format, why not accept it, there is nothing about it that will make your life bad just because it´s a successful format.