Read the above article.
It makes sense that we have it be 9-1-1, rather that the Britain 9-9-9. I can just imagine how many calls they get from children just pressing down a number or pressing the same number over and over - and then you have your occasional romp that you keep your foot on the phone pressing the 9 button.
I wonder in Britain what number they typically dial to get an outside line when they are at a hotel or at work? Maybe they don't. Does anyone know? I've only had to dial 9. And I could see a problem with people calling my cell phone which starts with 99. Which would be 9-9-9 (plus the rest) if you were dialing an outside line.