Well, apparently, it was originally conceived as "Waybac":
From
"On another note, we got a nice letter from the last living director of the Rocky and Bullwinkle Show, Gerard Baldwin, because he read about the "fantastic project". Our Wayback Machine is a tribute to their more cleverly named "Waybac Machine" which in turn was a reference to the Univac. Sherman and Peabody live on."
I think WABAC would have been more in style with the times (and Wikipedia seems to suggest the same) -- think of RUDI, Uniblab, etc.) but certainly "Wayback" is a colloquialization for folks with more limited imaginations.