You're not a guitar player, are you?
I'm a realist. When somebody does a cover of a song they frequently change the key, it's one of the things you do to make a song "your own", doesn't mean it's a different song just a different rendition of the same song. Functionally those songs are all covers of each other, yeah the re-arranged the lyrics a little, yeah they changed the key, but the points of similarity are much higher than the points of disimilarity. They're generic cheesy sweet innocent love songs, the keystone to everything that is sick and wrong in modern pop.