Mr.38th ;) (shall remain anonymous, as Batman ;)), I started on bass too.
My reason was patience, in learning chords, was not great at that early age.
I do believe, upon reflection, the rythm is more what got to me though. AC/DC after all is almost 'tribal' in there beat.
And thus,older,wiser and with accordingly more patience I caress 6 strings, yet I still find myself drawn more to the rythm playing than single note leads, the rythm again I tell ya :)