@oldredlion: Not entirely surprising: some ADSL packages have truly dismal upload performance, while mobile broadband seems to have much less of a gap between up and download. A few hundred K each way wouldn't be a surprising 3g service, but fast enough to match Paul's description.

I imagine the 3g/4/4s distinction is more to do with the age and usage pattern - serious heavy users are much more likely to upgrade or to buy the newest model, while less serious users will either stick to an older handset or buy the cheaper one new. I just passed my old 3g on to my mother, which she'll use for occasional email checking and not much else. Getting her a 4s would have been silly, but a 3g could be justified.

Even with the same usage pattern, the better camera will boost data traffic a bit: a tourist taking 100 photos on a 4s will mean more data than the same 100 photos on a 3g, just because of the extra resolution. Same with streaming video, I think, the 4s will take a higher res stream if available.

Then there's tethering - Three and O2 allow that for no charge on at least some plans, which wasn't the case for older handsets/plans; anyone who hasn't upgraded won't have that facility.