Yes - I briefly put my Gen1 mufflers on my Gen2 before going to aftermarket pipes. Fit is identical. Gen1 are 2lbs lighter each side and a slightly different sound. They don't have the 3rd and 4th cat converters in them.
Where did this rumor start? There are not cats in the GenII pipes. The GenI and GenII exhaust systems from the valves to the tips of the pipes are identical.
That is not true. In addition to a heated O2 sensor there are 4 cats compared to 2. I owned a set of both OEM pipes (I recently sold my Gen2 stockers and kept my Gen1 pipes). Gen2 exhaust pipes are 10lbs each, Gen1 are 8lbs each.
This was part of making the bike Euro-3 compliant or whatever that new standard is.
If the part numbers are the same now, it's because the new one has probably superseded the old part since they are interchangeable.