Yes, the MP-5 is a well designed SMG that has gained a great deal of popularity. It remains extremely expensive. The lack of need for magazine interchangeability and weapon optics has prevented the proprietary portion of H&K's products from being an issue.
H&K makes good firearms, they just do so using non standardized equipment and then charge a large sum of money for them.
Look at the G36, it is a great battle rifle. But it uses proprietary magazines. There is absolutely ZERO reason that the G36 should not also be compatible with the STANAG magazines. It already uses the 5.56 NATO caliber, why not the mags? They even can both use the beta C-mags. Furthermore it uses integral optics and only after years of pressure did it mount 1913 rails.
Special operations likes the MP5SD really more than anything. The MP5SD sports the neat integral suppressor that doesn't require subsonic ammunition (As the suppressor naturally decreased muzzle velocity enough to drop it below the sound barrier), making it easy to get the ammunition through standard logistics routes. Other than that, the SMG is unremarkable and requires annoyingly specialized parts. I imagine if they could do the same with the Colt 635, they would jump at the opportunity due to the increased part compatibility on hand and equal, if not superior, performance in the field.
True, but billions are spent on the Iraq war each year. Whats another one or two thousand to get a couple hundred special forces teams well equipped? All your other points arew valid.