In most cases, I guess it's just something which is overseen by developers, because they don't intend to play like this (and after all, they always say they make the games they want to play).
But that doesn't make it something which should work.
When I saw onlyuseMEblade in action, it looked interesting, but I could never watch his videos without thinking "wow, how can this be possible". A knife-only-nuke, for example, should just NEVER happen in MW2. But it does.