What are you basing this conclusion on?
I live in a substantial Comcast footprint and DirecTV's On Demand product is very competitive with it. I'd say DirecTV's might even be better after their HBO On Demand updates last year.
I'm basing it on the embarrassment that DirecTV calls On-Demand. Obviously I don't have any inside information.... I feel their pain - it's not like it is easy when you're dealing with a national distribution system rather than locally like cable... But they will have to change something if they want to keep calling it OnDemand and want to go head-to-head with cable OnDemand.
DirecTV can increase content - although they have a long way to go but the killer is how instant cable is.
DirecTV has more of a Demand Now-Watch Later system that requires a decent Internet connection to be usable at all.
With cable - at least around here - changing between OnDemand content is darn near as fast as changing channels. With Comcast I could take a quick look at 10 different OnDemand shows before I can get one OnDemand from DirecTV to start playing.... And that's with 50/5meg Internet speed.