First, the major difference: Rolex uses an in-house Rolex movement. Tudor uses an ETA-based movement, that, depending on who you listen to, is either highly modified, tweaked a bit or not at all. (However, there are some very early Tudors that use a real Rolex movement. And the Rolex Daytona used an ETA/Valjoux movement - as I understand it - just like the Tudor Chronograph)
While certain models of Rolex and Tudor share the same cases in vintage pieces, there are differences. My Tudor Submariners have a double lock crown, which according to JBHIII, is different from the Rolex triple lock crown.
On new Tudors, I believe no case parts are shared.
Rolex are generally - if not all - COSC certified for accuracy. Tudor is not.
Hope this helps.
I'm not exactly Mr. Rolex - and while I own four vintage Tudors info on the brand is hard to come by.
LMAO, guess scott and I were responding at the same time.