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I live with two girls who could get by on pretty much anything, but both have high-powered, hot-running Vista-based laptops for their internet. One buys clothes online, books cinema tickets and plays Farmville and Cafe world a lot (and I mean an unhealthy amount)... The odd time she opens a Word file or whatever but uses OpenOffice for that, or GoogleDocs if it's something she got in her email. That's the whole of it! The other girl looks up TV listings and uses Skype a lot, but doesn't even have an office suite installed. Granted, they're probably not the majority, but in my eyes they're two "average" users.
I don't doubt web-only people exist, I'm just not meeting them.
I think it is more average to depend on either MS Office or iTunes.