Silver and Gnome,
Urquell used to use a multi-cell pitching yeast. At one time up to 6 strains, down to 3 by the 80s. In the 90s when they went to a single strain, pure culture, the one yeast they chose to keep was, indeed, the one cerevisiae in the mix. Many of the US brewers may trace back to the two Siebel-banked strains from the two Ballantine plants, where they appear to have made their ales with a pastorianus strain (probable ancestor of 051 IIRC) and their lagers with a cerevisiae (probable ancestor of Chico.) The recent genome studies show a significant number of yeasts used for lager are cerevisiae, and a smaller but notable number the other way around. Also, there are so many methods available to manipulate the process to elicit different characters from yeast...
Upshot, I have my own proposal for how to classify lager or ale. I call it the "quack like a duck" method. It doesn't matter what yeast you use, what temperature or pressure or speed you ferment at, or how or even if you age it. If it smells like a lager, tastes like a lager, it's a lager. If not, it's not. How's that?