Perhaps but with the next gen aTV supporting the App Store, you have to wonder about app support on the current gen. We saw something similar with YouTube no longer functioning on older Apple TVs (because Apple no longer will update apps on those aTVs). Now, you could see either app developers or Apple killing off support of their apps even quicker since they now have a proper app store.I guess you are talking about the current Apple TV. There is no reason why it should lose functionality in the next years. And against what all the conspiracy theorists here might believe, Apple is actually quite good in support on legacy devices. I have an Apple TV 1 that still works brilliantly.
edit: I also have two Apple TV 3s and I fully expect them to function in the next two to three years. Considering for what I paid for them, that is very very reasonable.