xrayalpha,
Yes I am aware that wing loading and stall speed are also among the factors that determine what is a microlight and also that there is noting stopping anyone from paying a few mountains of cash to have a sub 450Kg MTOW aircraft certified and issued with a C of A.
However, the important thing is that JAR-FCL says that you can not claim hours on microlights towards those required for licence issue etc but that what determines a microlight is defined nationally.
Thus if Germany defines a microlight as being a max of 427.5Kg according to EDMJ then if EDMJ produces hours in a SEP with MTOW 450Kg (C42 UK Microlight) the those hours will count towards JAR-FCL requirements.
As I said, hopefully EASA will end all these differences.
Regards,
DFC