But really, developers need to keep up with the updates because new iOS with idevices coming yearly...gotta keep up with bugs and compatibility.lol
As far as the you can download it forever thing....that is not always true. I had downloaded Fluid & Fluid2 back in the day...like iOS 3 days. The developer didn't renew his developer account and for years I wasn't able to redownload it. Recently he signed back up and I was able to redownload it...but I went a few years without it. Let me tell you....you can really miss an app that plays the same song and lets you touch a cheesy water effect. I don't know how I lived without it. Fluid 2 lets you toss euros! There also was an app back a few years ago that Apple pulled and was not able to be redownloaded. People were selling devices on eBay for big money because they had it installed....I can't remember what it was.
But make your peace with "I Am Rich" before it disappears forever. That one day you have to reset the iPhone.....that's $999 you'll never enjoy again. But I am sure that app has already paid for itself 220 times over.