Joey - I believe the unlimited ammo "glitch" was actually someone who had modded their version of the game and played it online, then thus distributing a "virus" of some sorts. No one knows how the infinite ammo glitch came about but it wasn't a plain exploit/glitch like the Javelin and other glitches.
As far as the private matches are concerned, that's something should never have happened in the first place and I agree there that they needed to test it more thoroughly.
On a good note however, I just completed the last achievement in the game

So now I have 1000/1000 GS for it (from what I recall only have completed 2 games fully, this one and the first MW

). The hardest mission was the explosive juggeernaut one and wetwork (did wetwork by myself)
EDIT: They're already working on tweaking 1887's and fixing the existing glitches that we have been talking about just now:
Infinity Ward