I got this question recently and I thought maybe it was worth answering publicly because I know there are a lot of iPad 1 owners out there and I know it's frustrating that more and more apps aren't compatible with the first iPad.
Most importantly, I want you to know that I did not take this decision lightly. An iPad is a big purchase for many of us and these devices are made so well that they still look and work pretty much like new for years. I get that it doesn't feel right to "have to" purchase a new one just so you can get the latest software.
The thing is, the tablet market is so new and still changing so fast that it's not really so shocking that the first wildly popular tablet now can't run the latest operating system and is therefore close to obsolete. After all, it's been more than two years since Apple discontinued selling the iPad 1. (For a more detailed explanation, you might want to read Marco Arment's blog post about why the iPad 1 can't run iOS 6.)
It might be harder to understand why a developer (like me) would decide to release an app that requires iOS 6, when there are still lots of people out there with iPad 1's that can only run iOS 5 and would still really like to buy this app!
It certainly is possible to write an app that runs on both. I've done it, actually. My first app, Cross It Off!, launched in early 2011 (before iOS 5 even came out). The upgrade to iOS 5 wasn't too difficult and I was able to require iOS 5 fairly quickly because pretty much everyone was able to upgrade their devices to iOS 5.
The switch to iOS 6 caused a lot more headaches for me, which have taken a long time to fully iron out. Partly, that's because I was also writing a new app (Knittrick) and going to graduate school and raising two small children at the same time. Whee! But I can definitely tell you that it would have been an easier process if I had just said, "Sorry, but you have to be running iOS 6 to use this app from now on."
That's because little irritating things change from one iOS version to another, things under the hood that a customer will never notice... unless an app fails to deal with it properly. One case in point: the way you allow or don't allow the screen to rotate when you rotate your device changed in iOS 6. Changed in a way that totally broke a small but important feature of Cross It Off! (you can lock the screen so that when you're shopping, your list doesn't rotate all over the place just because you can't pay close attention to keeping your phone level while you bag the apples). Unfortunately, fixing it for iOS 6 then broke it for iOS 5! Which required more fixing. It works now, on both, but it was a real pain to get right when I had other priorities on my plate.
On top of that, each new version of iOS has a bunch of technical goodies that make a developer's life much easier or allow apps to do things that previously could not be done. Again, these are things that a customer probably won't notice. But they make a big difference to the person writing and maintaining the code. For example, Knittrick uses the new layout system, which makes it easier to make to app look and work well on screens of different sizes and shapes. It also relates to how the animations are done (for instance, how the calculations area slides up to make space for the keyboard and how the menu opens and closes). That new system simply won't work in iOS 5.
As I continue to build my business, I have several more app ideas that I hope you and others will enjoy using. I know from experience that I have to plan ahead to make maintenance of all my apps as simple as possible so that I can keep my existing apps running well, while still having time to create new apps and cover all the other aspects of running a small business.
With all that in mind, I will do my best to keep my existing apps running on any device that could have run them when they were first released. And I will require the most recent version of iOS for new apps.
I hope that helps explain the reasons behind these decisions, which I know can seem arbitrary from the outside. Thank you for reading and thank you for your interest!