I'm not sure why the GP said his iPhone 4 won't upgrade past iOS 5, but it's worth noting: while an iPhone 4 can be upgraded to iOS 7, actually doing so is a bad idea unless you want your phone to run slow as molasses. You'll be much better off on iOS 6 or 5.
(I suppose there may be a security argument for upgrading as far as possible, but it's not like iOS 7 is up-to-date either. If you're concerned about security, you shouldn't be using an iPhone 4.)
Sure. But if you are making an app for say a government service that has as a requirement to reach 98% of mobile users, and you reach the goal if you count compatible devices (not people who choise not to upgrade) then it helps.
Correct, sorry, didn't bother to look at the time. It is 7.1.2. The point still stands, it's old and I'm probably in 0.1% that the article left out in iOS markets.
(I suppose there may be a security argument for upgrading as far as possible, but it's not like iOS 7 is up-to-date either. If you're concerned about security, you shouldn't be using an iPhone 4.)