I've seen quite a few Maiden's videos, pics or concerts and never saw them being dressed in a biker-style. Though I admit I haven't seen any videos or pics from the beginning of their career, when DiAnno was on vocals, but I highly doubt they wore leather.
Guys from Black Sabbath usually dressed similar to hippies back then. Never saw them in leather.
Leather and biker-style mostly make me think of Rob Halford, whom Ob mentioned. He also used to drive Harley during concerts (and I'm positive he still does). Though where did the idea come from, that I don't know.
That's just random info from me, a guy who listens to the music played by musicians, and whom the way those musicians dress does not concern.
