That would be true in open terrain, but in the cramped hallways of an Iraqi residence the M4 is a little bit too long to bring to bear quickly. That's one reason for the sudden interest in the 45.
I read an account of the TORA BORA campaign of two SpecOps guys clearing a cave complex from one of many directions. This team took the very cramped area and others were handling the other approaches. They rounded a hairpin in the tunnel and it opened out to a larger cavern, lit by a lamp and showing three "tango's" studying a map. One seated, two standing. Ak's were either slung or leaning against an unoccupied chair. The operators get within say thirty feet in the gloom outside the lamp glow before they're detected. All hell breaks loose. One operator has a M9 Beretta and the other an H&K MK21. The guy seated has the closest grab to a weapon, he catches rounds from both operators and slumps over. The guy on the right is taken by the H&K. One shot he goes down. This operator automatically swings his weapon to back up his buddy. THAT tango is still on his feet, the Beretta is still speaking and the H&K has time to join that conversation. That tango had taken three hits by the time the H&K got into the action and he was still in the fight.
I dunno if these were Delta, Rangers, SEALs or what. Because the presence of two different types of weapons and calibers seems to suggest either a "personal weapon of choice" in contravention of the regulations or a loose unit TO&E. That would suggest the D-Boys to me.
The point is, I learned at the Infantry Officer Basic Course that if you have to transition to a sidearm under most circumstances, indeed you did something very wrong! However, there are times when a handgun is the best possible solution. Sometimes you can't just toss in a grenade. Sometimes you've got to round that tight corner and use a handgun to best advantage. If I'm slicing the pie around a corner, I'm wanting a 45 and not a 9mm if I can help it.
114: right on!
The only reason to use a handgun in combat is to fight your way to an available rifle.