the difference (for me at least) is the price. there are many games and apps that i would like to download but i cant spend 6 and 7 dollars for an app. if they lowered it to 1 or 2 there would be a lot i would buy. but i have to buy apps for my iphone and ipad and i cant afford apps for all three. the iphone and ipad come first as they are my mobile devices and i use them the most.
You've pretty much summed up the reality of all this.
Note that before the AppStore was introduced with low prices for mobile apps, we were paying $20 to $60 for most "computer programs." We seem to be finding it more difficult to justify that now, not simply because we might find expensive (despite prices not changing much), but because our mobile gear is becoming our priority for average, daily use.