Okay, everyone knows that Bolters are, basically, useless in normal games. They can be somewhat effective at range, but that's only when the squad hasn't moved and isn't inside a transport. How often does that happen? The alternative is to shoot on the move, but then your shots are limited to 12" and you can't assault. So, the squad charges forward, shoots, and prays that they eliminated the threat. Else, they get shot and charged next turn. But, how often does 7 bolters, a bolt pistol, and a meltagun eliminate the threat?
15 bolt shots = 10 hits (avg), 5 wounds (avg) + 1 wound from the meltagun, so 6 wounds that are possibly saved if the enemy has 4+ or better saves. Against any sort of horde army, that's just not good enough. Against any combat specialist squad of 10+, that's not good enough.
Lets say that you do those 6 wounds and kill 6 orks. That leaves 18 orks plus a nob. They move up 6", return fire for 46 shoota shots and 6 big shoota shots, 15 + 2 hits, 7 + 2 wounds, 3 dead marines. Then, the 18 boyz and nob charge into assault and it's all over.
So much for the Emperor's finest, eh?