Since these days a very high percentage of bike frames are welded up in China or Taiwan, I would be willing to bet that many brands actually have the same frame.

Besides, with a certain spec, what would be different? Would there be a rep from a certain company be in the factory to give a frame a hug and a kiss make it special for that company?

IMO it comes down to what you dont know wont hurt you. I have tho always wondered what a generic frame from China actually cost the bike manuf here. Does anyone know.