It really is. It works most of the time for the same reason it works in war, you have the element of surprise. In a population of ordinary citizens you aren't likely to encounter much trouble kicking in doors at 2am. It works for criminals after all.

But things are a little different in the US because there are lots of keyed-up gun owning vets that spent most of their military service conducting urban warfare.

Put simply, you cannot just roll up on me like that. Just knock on the door politely and I'll come out and chat. Kick in my door like a home-invasion robbery and I'll follow my training without thought.