Are App Developers Obliged To Update Paid Apps?

I recently upgraded to an iPhone 5 and, upon reloading all my apps, noticed that one of the more expensive games that I'd bought ($7!), had not been updated since I bought it almost two years ago. Not even an update to support the iPhone 4.

Now, this company still makes games. If I've invested in a number of their apps, should they be at least obliged to update them to the latest version? Their games are still on the store for $5 each!

Without naming names, these are popular games. I have bought quite a few games and even the cheapest of the bunch are updated after ever major iOS update.

What gives? I'd like to hear both from app developers and consumers!