What's so good about apps? Let's look at them from the buyer's perspective.
Buying an app is quite similar to buying stuff on the Internet. Buying on the Internet is a bit similar to buying in a store. It's entertaining and exciting and safe if you choose a good vendor. It's shopping and most of us like it, unless we actually love it.
When you're done, you have another nice icon on your favorite device and some great functionality that can bring pleasure for as long as the device lasts and even on future generation devices. You can use the app whenever you like and as often as you like. It doesn't wear out and it won't cost you extra. Thanks to how mobile your device is, you can take it with you when going on holiday, going to work or going to the bathroom.
As if the above wasn't enough, apps are cheap and even free of charge.
What can you do with apps? Short answer is: anything you can do with a computer. What can't you do with apps? Anything you can't do with a computer. That includes brushing you teeth, walking the dog and doing the dishes.
The future for apps looks great. Future Internet browsers mated with lots of attractive web-apps is the only visible challenge. The future for smartphones looks great too.