Technology isn't in Extras.
The only reason for one format to win over the other, is corporate strategy. Sony is doing it's best to have their more expensive, yet technologically superior product out there by targeting family entertainment sector more virally. Playstation 3 came with a BluRay-rom, and enough hardware to play it in full resolution. What does HD-DVD have?
The example above is a technological benefit, and I totally disagree with calling featured extras same. What's so technological about having the actors talk about the movie, or having 400 hours of bloopers footage? Albeit in this particular case, the latter might rekindle the internet's "Spaaartaaa!" fad.