Daeld I'd imagine they're predominantly English speaking because most scammers are based in India and most of the "educated" Injuns speak it (as well as Hindi). I suppose it's also got a lot to do with market share given the number of computer users etc. in the US, Canada, Britain, Australia, South Africa and so on; plus the fact that we're generally considered more 'cashed up' (and gullible perhaps?)
The Russians and other East Europeans also have a pretty good reputation for scamming I think, but there are too many juicy targets to go after in India before I'd worry about them. Anyhow, I'd miss all the fucked up grammar like: "Sir, I'm call from Microsoft Tekneekul Departmen about your wirus on compooter".