I love Steam, but they don't police it as much as you think.
First off, pre-orders are always problematic as Steam doesn't know if a new game is going to be good or an unfinished tech demo that was released one year too early, which was the case for a game I pre-ordered last year. If it's bad enough they'll do refunds, but you need to push them and they won't always grant them if you don't ask in a timely manner.
More troubling, they sell games that they know are broken. Full Spectrum Warrior is one example that I can think of. The game tries to resolve a no-longer existing address hundreds of times a second and lags horribly. It's easily fixed but Steam support doesn't care because it's not Valve's game.
Steam does a lot of things right, but it's very much a buyer beware situation, and for higher stakes than a $0.99 app.
I was assuming the meaning for that statement was on that point, not on a developer supporting an 8 year old game.
I think the big difference is that people buy a game on Steam to be immersed for a few days, yet people buy smartphone apps to bridge the gap between two Twitter mentions or subway stops.
Steam for example has none of the same problems as the app store because they very actively curate, and they don't let the riff raff in, which erodes consumer confidence in shopping in the store.
Apple on the other hand, actively structures their store to drive down prices. The busiest, most profitable placement in the store is the top volume charts. Which naturally means that developers will lower their prices to climb the charts and get better placement. Additionally they don't curate much, or allow demos, so consumer confidence that they will like the app they buy is low.