I think this is funny, but also it makes sense that Goku keeps getting stronger. As it gets explained in the anime, Saiyans grow stronger as a result of near-death experiences. Which Goku has in spades. Even actual death experiences.
All you guys are raising good points, but what I think is important to remember is the gohan always seems to hit a ceiling in power. Yes, he was stronger than goku briefly during the cell saga, even the buu saga, but it was goku who ultimately defeated buu. Also, even though egeta is also ssgss, Goku still got there first. Vegeta couldn't even go SSJ4 without Bulma's science. Goku has limitless power. Everyone else seems to have caps.