Some companies don't pay _taxi_ travel costs if there is a cheaper alternative (e.g. shuttle busses)

Good point. I try to take public transport on business (and personal) trips whenever that's reasonable (which is subset of those times when it's cheaper).

In many foreign countries, the taxi is so much easier than trying to figure out public transport that the taxi wins. In many US cities, public transport doesn't get you close enough to be reasonable alternative, even though it would be less money out of pocket.