MP-5's
Current military doctrine with all services 'Spec Op' units [SF, Delta, RDF, SEALS, Para-Commando, etc] now utilized the P-90 as an alternate machine pistol. Uses the same round an M-16 does [5.56], is a more compact 'bull-pup' weapon design with a better reliability history [than the M-16 - the MP-5 is a great weapon, IMHO], abidexterous saftey [nice feture] and a 'smoother' outline - not as 'harsh' lined as the outline of an M-16 or MP-5, making it harder to see against a motteled background, like the boonies.
It's the last, however, I believe, makes it a poorer choice of weapon for the 'show' as it doesn't stand out well in production. Good for real camo in a real field environment, bad for filming.
I think, with the show, it's their desire to reflect 'real world' military reality. I had a chance to talk to Tom [the shows Air orce advisor at the Con] andhe and the studio work hard at keeping things as accurate as possible and a command like SGC would have all the current 'goodies' to choose from.
That's MHO - and that of my husband, the US Army Airborne guy with the Green Hat ...
Rowan