I was hoping you'd find my red herring
They look like mx bikes but they are not! The suspension is much more supple, the gearbox is a wide as opposed to close ratio, they have a different rake and trail and the power delivery is very much softer.
A couple of years ago I saw a pic of the KTM that Cyril Despres rode at Erzberg and lo'! It was without expansion chamber! Just a bit of straight'ish pipe just like a trials bike. Heaven knows what they had done to the porting. Now Cyril's also a pretty good trials rider (French junior champ I think) so he was probably looking for some trials bike characteristics. There are certainly times when you'd need the pure power of an enduro bike but, in the case of extreme enduros, I think you could sacrifice some of that power for a bit more flexibility.
It would be nice if somebody like Paul Bolton (again a bloody good trials rider turned extreme enduro guy) could chip in here.
P.S. Juha Salminen was Finnish junior trials champ. Do you see a pattern here?