Developers used to be motivated to release the next versoin and make you buy their app all over again. The upside is now you dont have to buy a bunch of applications for $120 (a year if you always want the latest version) and you can just pay as you go. But like you I have had a few subs that ran over and now I avoid where ever possible.

Adobe were the last to annoy me, previously I am sure I had paid up for a few months and then unsubscribed. Now its a 12 month commitment when you take out a subscription.

Off topic; but if you want a flight tracker, and like to tinker, try feeding flightradar24 (or any of the other), while you feed them you get their full membership. A pi and a usb tv card are all you need to get started!