It's not tautologous - many single track vehicles use a rear fork to join the frame to the rear axle. In fact, on STVs with rear suspension, arrangements other than a trailing fork are the exception rather than the rule.
But is it common on bicycles? A rear triangle isn't a fork is it?
On a conventional rigid bicycle, the rear triangle is a pair of forks. If you're going to get upset about any tautology, you should be wailing and gnashing your teeth every time somebody refers to a front fork as a pair of forks :)
It's not tautologous - many single track vehicles use a rear fork to join the frame to the rear axle. In fact, on STVs with rear suspension, arrangements other than a trailing fork are the exception rather than the rule.