I can think of at least one very important use case for 3G enabled iPads - business travelers. Maybe it's different in the US, but here in Europe I often find

I can think of at least one very important use case for 3G enabled iPads - business travelers. Maybe it's different in the US, but here in Europe I often find myself in hotels without wifi - or with wifi available only in the lobby. The fact that I have my iPhone with me at these times has been very useful, to say the least! I would pay over the monthly fee without hesitating when I find myself in that situation, even though when I'm in my normal routine I can see the OP's point that wifi is normally enough. The 3G option is for when it isn't enough, which is why it's so handy to have as a pay-as-you-use option.