I don't think it's really an issue unless it's Soviets with their cheaper 6 man crews...
Consider 2 cases:
A HMG is being attack by 2 infantries first gets pinned while the second one perform a flank maneuver. Second get into place but the first has to retreat because of taking casualties and damage. HMG also retreat once it is flanked. Since the HMG can reinforce faster and has taken less damage it can return to field faster although it was outplay...
HMG near reinforcement point the HMG (unless under very heavy fire) can reinforce faster than the enemy can kill squad members.
Lastly consider infantries:
Compare Obers and Shock ober must retreating after taking 2 casualties of fear of squad wipes shock can stay until they take 4 casualties. Yet due to different reinforcement time shock can return in the field about the same time....So shock troops actually have allot more fighting time than obers....and thatn makes them a better investment regardless of other statistics...