Thank you all for the replies.
I am sorry, I didn't want to start an argument, I was just going by the weights on the brochures I have for the equivalent HP tractors (M9540, MF4709), and I wondered why the big difference.
If Kubota really are referring to shipping weight without wheels, that could explain it, I know there are cast centers or pressed steel centers options which would make a big weight difference.
I hope to have a look at some tractors in the next few days, one plus for Kubota is they have a dealer 15 min drive away, the other dealers are at least an hour and a half drive away which is still not too bad.
I have some boggy low-lying clay country where lower weight may be an advantage? I guess you can always add weight for traction when necessary?