I don't think this is the case either. I've not exactly seen all of London and different areas won't be the same, however it is really busy and people are jsut used to getting there heads down and working, which sin't a bad thing. I don't really think you need to be talkative to be friendly. Here around here I don't find people any friendlier. People may communicate with others more, but it's usually being nosy or whatever, I find. Like they try to become part of your life and whathaveya, causing trouble, If that makes sense. It's not the only way of being friendly.
I don't think keeping yourself to yourself is bad at all. it doesn't make you any less friendly. I've not had any problems with people in London where i've visited. It's quiet, people aren't loud. I suppose I like the seriosuness though, it's all clean there, no people dossing about causing trouble, you know. I can't exactly speak for the whole of London but I guess everywhere has it's good and bad points and friendly and non friednly people, although, for some reason with the work rate and stuff of London, it's more my thing.