Lets start with a definition… According to dictionary.com…
- a combination of statements, ideas, or features which are opposed to one another.
The exemption is limited to travel in a vehicle licensed by the relevant State or Territory to operate as a taxi. It does not extend to ride-sourcing services provided in a vehicle that is not licensed to operate as a taxi.
When considering whether Uber drivers should be treated as taxis for GST, the Commissioner said they should and won a Federal Court Case saying all Uber drivers are taxis, forcing all Uber drivers to register for GST from their first dollar, rather than $75,000 turnover (Uber BV v. Federal Commissioner of Taxation  FCA 110)
So when being a taxi is good for taxpayers (FBT exemptions) the Commissioner says Uber is not a taxi, but when being a taxi is bad for taxpayers (having the remit GST from the first dollar earned) the Commissioner says Uber is a taxi.
The worst part is that, when he is made aware of this contradiction he puts out a discussion paper asking what he can do. The answer is easy… avoid contradictions.