Apple should really follow Steam on the pricing part. Meaning that they should implement a "limited-time-offer" feature in their app-store, offering some apps in reduced prices. Otherwise, they are indeed fall back in comparison.
Applications
do go on sale in the app store for temporary periods of time. It seems to be up to the developers as to what the price adjustment will be, and for how long it will remain in effect.
The only area where the App Store falls behind Steam in that regard is that the discounts aren't advertised. Steam puts up a green icon indicating what percentage off the game (or application) is; the App Store just shows a price, and you'd have to go to the product's page to see the developer mention that there's a temporary discount in the description.
I have mixed feelings about Steam's sales, though. Sure, I buy a good number of games through them and appreciate the opportunity to save money (or rather, "save" money, because I've probably spent more than I normally would have, and now have dozens of games that I have yet to play), but I don't like some of the things that it has done to the community. In visiting the Steam discussion forums for various games, I've run across countless posts of people whining about the price, demanding that the game be put on sale... and then when the game does go on sale, they whine about the percentage not being higher. We're not talking a $60 game, either; these games are usually $15-20.
I also worry about the developers. I have an abundance of games at this point, but not an abundance of time; with my gaming backlog, I could probably not buy another game for 2-3 years and I'd still have new games to occupy me. As such, I have no problem waiting until a game is on sale for just a few dollars before I buy it, further contributing to my backlog. It sounds like a lot of other gamers are finding themselves in similar situations. Steam's sales occur predictably twice a year, so even if there's a newer game that I want closer to the front of my queue, I know that the years-long wait need not be necessary: wait a few months to a year and the game will likely be on sale. Are the developers making less money because people are getting into that trend, and refusing to buy anything that costs more than just a few dollars?