PDQ, not that I relish the thought of defending the Yankees, but the above figures translates into 123 seasons for the Giants, 105 for the Yankees.   

If my math skills are working (and please check my figures because I could very easily be wrong) - based on average wins per season - the Giants would have 81.60 games per season and the Yankees would have 87.54.

I don't think you can give extra points to the Giants just because they have been around longer.