Attendees looking to invest in new companies probably like DEMO because the presenters are convinced enough they have a great product that they'll come up with the funds to go there. They're showing both a solid demo and enough leadership/backing to procure the money to play.
At TechCrunch50, investors can see a different sort of startup. One who has a lot of potential, but may not have had the drive/opportunity to gather any real money in the first place.
From a purely investment risk perspective, companies that are already finding capital with a good idea and a good demo have more going for them than startups that merely have an idea and a good demo.
Because of this, perhaps VC firms (and big business partners) like DEMO more and angels/seed funds like TechCrunch 50 more.
(again, just playing devil's advocate here)