Of course, but all over the world is not needed: a company with a presence in whatever country you go for holidays/work is enough, so an app with a nearly global presence will get all the travelers' money automatically. (For instance, I never use Uber in my home country, but at the moment I am in Romania, and the fact that I could call a cab at the airport in a new city with zero hassle is very sweet; I imagine that people coming to my country and not in the know about the local taxi market will be in the same position.)
If there is one place in a country where finding a cab has always been straightforward, that's an airport. I mean, it is easier to find a cab by walking through the airport doors than avoid the cabs there :-) That's really the place where Uber & Co add zero value.
> That's really the place where Uber & Co add zero value.
In my opinion, the added value with Uber at an airport is knowing the price up front. That's not always possible with whatever driver is first in line at the taxi stand.