It really depends on individual examples.
When I think about it, some of my PSN game purchases were played more than the typical BD based retail game, but this is not the norm.
I'm not sure how many hours I spent playing Scott Pilgrim Vs. The World, but it's safe to say that I got more play time out of that $10 title than most of my full priced retail games. I think I also played Ratchet and Clank: Quest for Booty more than most retail games even though it was short.
But anyone who ever finds themself being "done" with a game they bought as a new release at full $60 retail price after one play through or even less than 10 hours should really reconsider buying $60 games period if their dollar/entertainment hour ratio is such an issue.
There are alternatives: renting, gamefly, buying releases when discounted, buying releases when they go to "greatest hits"/"platinum hits" pricing, and of course, inventory clearing sales at various retailers (when they stop stocking games, they usually sell the remainder of the inventory for $20 or less).
Either way, I wouldn't be satisfied just playing DD based games on consoles; very few of them offer the same experience.
