The B.A.R., Bren, Type 99, DP-28, Brenda 30, and a handful of others that escape my immediate recollection would disagree with that.
In fact, the German LMG's were unique, as they were more or less the first folks to come up with the idea of a general purpose machine gun that could be used for anything from squad LMGs to support MMGs to coaxial guns on tanks to hull guns on aircraft. The MG34 is the odd one out that uses a belt here.
Again, I'm still not understanding why you'd want to expend your limited ammunition before reloading shooting at walls and dirt. If you see -motion-, open up at it. It doesn't have to be a clear target. Maybe that's where I've been making the mistake in my explanations. You don't have to see a big obvious guy with a "kill me" sign on his head, but if you see a rifle sticking out from around a corner, yeah, you shoot at that to try and penetrate his cover and let him know that he's not as sneaky as he thinks he is. He'll think twice about popping out to shoot you.
However, you -stop- after that. Don't waste ammo just shooting at the wall. You've made your point, he knows you see him, keep an eye on that spot and go back to hunting for targets. Don't zero in on the first sign of life and pump all your bullets into it. Someone will pop out as soon as you stop to reload and kill you.
You want people to know there's an MG on the battlefield, but not where or what he's doing. You let them know "HEY, I SEE YOU" and then you wait for them to try something. You don't sit there and keep shooting so that the guy you -aren't- shooting at can identify your muzzle flash and kill you.
He's suppressed perfectly if you do it right. He can't peek out to try and see you, because you'll kill him. He certainly can't try to cross the area, because you'll kill him. If he tries to fight back, you'll kill him. He's well and truly suppressed, and without some help from his squadmates, a smoke grenade, and maybe an artillery barrage, there's no way he's getting through your line of fire, and he knows it. He's either going to go back the way he came and try and get around you or try to coordinate a way to root you out of your hidey hole.
Other than those two points the rest of the post is spot on.