Forgive me if this is out of place, but it strikes me that the E-G-c inversion allows the melody note to be on top and leaves an opening at the bottom to drop in a bass note, making it possible for both to move around a bit, without stepping on the guys holding the chord down---

The other thing is that the voices on the E and G are singing a minor third interval, which is a very intuitive thing, and sounds "right"--It also makes a it possible to do a simple sort of "chase" through the 1-6-4(2m)-5 chord progression, as follows: two voices start on E-G for C, E stays put while G moves up a single scale step to A(for A minor), A stays put while E moves up a step to F, then both move up a step together to G and B for that penultimate G chord--then B stays put while G drops a major step to F for the G7--Once a group of kids know this trick, they can use it over and over, with the melody sailing above and a the bass punching in below, and even add simple rhythmic variations(such as Wa-Wa-wa instead of Do-do-wah)--