It is well known that lower response times increase conversions and reduce abandonment on any website. There is absolutely no reason for a website to cross the 1-2mb threshold unless it's a huge web application, a game or image-based app, or is serving you hi-res photos.

And, obviously, websites are accessed from all kinds of connections. Not everyone has a generous 3G plan, and even the US doesn't rank that well in average broadband speeds.