Lots of times, when a game indicates "it'll only run on Ubuntu", it means, "It'll probably run on all linux systems but we only know about Ubuntu and we don't care to test it on anything else, so if it doesn't, that's your issue."
Nice to see people still replying to this. Well, this is what I've learned so far. The launcher does indeed help, but what I didn't know what that all I had to do was right click on the downloaded app and right click on it, find the permissions tab, and check something like "allow executing file as a program" or something like that. I was able to run the launcher, and it made it easier to download and install games. I don't even need the launcher now, but it's nice to have.
Anyway, I do agree with your point there. I love Linux now, but it's made for some frustrating moments here and there.