A lot use 1. A lot use 2 or 3 (adding a single lager yeast and a single belgian yeast). They would rarely use more than one yeast in the same basic category as they almost certainly practice repitching.
I think you will find that most commercial breweries use the same yeast for all their beers. Obvious exceptions would be those that brew both ales and lagers or specialty styles like Belgians or super high gravity brews such as some of the Sam Adams and Dogfishhead offerings.