i´ve heard through the grapevine that the UK government wants to get rid off the British Marines and Paras. the logic they bring is they are infantry and just the same as any other UK Infantry Unit. true..(to a point) the modern day role is infantry and i remember being told from a Guy who was a Guardsman in the 60´s that they also were airborne trained. I think it´s more tradition and pride.
I can't comment on your guys stuff... but there is a significant difference between US Marine infantry and US Army infantry. (Regular Army infantry, the Army Airborne guys I've met were much more gung-ho than the regular straight legged grunts)
I think, as you alluded to, that it has to do with the way their training has evolved over the years, and tradition, pride, and a large part probably has to do with the way the Marines indoctrinate their recruits, the Marine Corps really try to make us mean, (like someone who trains a fighting dog.)
I think it also has to do with the type of individual Marine infantry tends to attract.