Same complications, sure. However, a Rolex 3135 movement is a better movement. It's not about tolerances, it's about materials, design, construction, etc.
http://www.chronometrie.com/rolex3135/rolex3135.html
Most people reckon it's better than the ETA 2892A2, which is an order of magnitude better than the ETA 2824/2836 we get in our reps.
If you want to go Omega, the movement in a Planet Ocean is significantly better than the 2824 we get in our reps because it's a highly modified 2892 with a Co-Axial escapement.
IWC sometimes make their own movements, and where they don't, they change a lot of parts for much higher quality parts. A 7750 from an IWC 3717 will be much better than one straight out of the ETA factory. It's like a blueprinted engine with strengthened parts used for production racing is better than what's in your car.
Breitling, however, use pretty much the same movements as we get here, so on that one, sure, you're not getting much more by going gen, but Breitling gens are by and large cheaper than Rolex or Omega gens.
In conclusion, the movements used in Rolex Subs and Omega Seamasters are considerably better than what we have access to in our replicas. They are also considerably higher quality than their cheaper competition, like Tissot, Breitling, Sinn, Fortis, Longines, etc.