Sure, but, for example, Uber in London is not in the taxi business, but that of the minicabs. Minicabs don't need the taxi license. However, Uber does need to comply with TfL rules.

The really disrupting thing here is the ability in ordering the car from the mobile phone, and the frictionless experience. This is what is making the taxi obsolete. Now that black cab drivers have realised of the threat, they want to consider all others equals, when before they where happy living with Addison Lee, et al.

PS: travel agents do need licenses to sell airplane tickets, and have bank guarantees, etc., just to gain a fee. Pass through websites which earn a fee, like the travel agents, don't.