So many popular songs sounding so similar? I'm sure one factor is that there are certain harmonic progressions (ie, 'chord changes') that tend to be aesthetically pleasing to large numbers of people, so they get used A LOT. This in turn greatly reduces the possible melodies (or 'sequences') to only ones that are compatible with these harmonic progressions.
A ten-note melody utilizing just two notes? Not exact, but close enough to make a point - in the main theme from "Jaws", significant sections, more than 10 notes in length, utilize only 3 notes. Yet in that context it worked very well, and was extremely successful...still well-known, after almost 50 years. A 'melody' (or sequence, motif, theme, etc) doesn't need to be purely aesthetic or 'pleasing/entertaining' to be useful.