Yeah good point. But I think Googles.com predates Google the search engine. Plus two companies in different industries can use the same name. Apple (the record company) and Apple (computers) both coexisted for many years with their individual trademarks, which happen to be identical. They only ran into trouble when Apple computers started getting into the business of selling music.
When you do a trademark search, you can see which classification (industry) the trademark is registered for.
RJ - We all know Apple (the computers) never sold music, they just did data transfer... just ask the judge
As far as the original quesiton, plural/single, it does not matter. A test of TM law is "similar or confusingly similar" using plural/single of a TM means that it could be construed as comfusingly similar; thus, could be found violating TM law.