The Seneca in the USA has a higher MAUW than a Seneca in Europe
There is no physical difference in the aircraft. European Senecas are invariably certified at 1999 Kg to avoid Euronav charges (> 2000 Kg).
The usual MAUW for a Seneca is 4570 lbs (2072 Kg). I assume that the operators have done their sums regarding the "loss" of 73 Kgs useful load verses Euronav charges and decided in favour of the former!
You could operate a european Seneca at the factory MAUW - There is nothing stopping you other than the paperwork - but you would then be liable for the charges