What is the actual reasoning behind this?
The reasoning behind it is that if there were no such restrictions there would be chaos and carnage.
Human nature is such that when remuneration is involved ambition and greed WILL override all other considerations. In common with most laws these restrictions are "designed" to protect the many from the few for the greater good.
From a pragmatic perspective it's not worth the hassle mate. For reasons already stated in this thread - if you go much further than BEagle and others state your fare paying 'passengers' WILL at some point drop you right in it when they start moaning, refusing to pay up or turn nasty demanding their rights WHEN you screw up or are subject to some sort of 'misunderstanding' over your presumably non existent terms of service.