Its too funny, theyve been saying that about the .50 since Vietnam. "old weapon" blah blah blah. And every time they get in some situation where they need vehicles or light cover (improvised bunkers, people in buildings, etc) taken out - the ol Ma Deuce is the most economical way to do it. Bring a few HumVees with pintle M2's and you can chew up a LOT. You'll saw through a concrete block in no time, so unless the cover is solid with rebar and all, it wont last very long.
Try fiddling with that with M16's, 249's or even the 240. And if the target is a few hundred yards away the bloop gun wont be that accurate. Besides, using the M79 effectively requires some practice, same as anything. How many people today have much time with one of those?
Yeah, that ol .50 will be a round a long, long time. Nothing (Western) exists which fills that role so effectively - it aint a rifle and it aint a cannon. But what it does, it does well.