"You just killed 10 guys in a row. Here's a bonus that lets you kill another 10 guys in a row to get yet another bonus!" It just gets old if you're on the losing end of that gameplay mechanic.
Yeah, that just doesn't happen. Assuming you're able to kill 3 people without dying, you get a recon plane, which is great as long as everyone on the opposite team doesn't have camoflage enabled - but really, it only tells you where people are. It doesn't help you kill them. Then let's say you kill 5 without dying, you get artillery, which rarely kills more that 3-4 people even if you place it well. Then, you kill 7 people without dying, and you get dogs, which, fair enough, can yeild a fair few kills, but it's hardly a game breaker.
I don't necessarily disagree, but I do find the artillery annoying. I've always hated explosion spam on CoD, it's my least favourite thing about the game series, and the artillery and multi-frag perks just make that worse.