But it's not meant to be a replacement for a desktop, though.
It's mainly for content consumption (although some people do use it for productivity), and it has portability and instant use that a desktop doesn't have.
Portability outside *and* inside the home.
I can't use my desktop on the sofa, or in bed, or take it away with me.
I could use a laptop or netbook for those places, but they'd be heavier, have worse battery life, and not have the instant-on convenience of a tablet.
When my wife is in control of the TV, and watching Strictly or something, I can relax on the sofa with my iPad and watch my TV programmes, play games, surf the net, etc.
If I'm hogging the TV to play Skyrim or watch a film, she can go off and watch/surf etc. on her iPad.
Although I only have a WiFi model, I still use it on my travels. We went to London on my birthday a couple of months ago, and both took our iPads. Played Scrabble on the train there, watched videos on the train back. Need the internet? Just tether to my phone. I spent a weekend in scummy Blackpool back in May, five hours on the train there, five hours back. The iPad got a lot of use watching videos and surfing the net that weekend, on the train and at the hotel. My wife's been going to London a lot recently (she aims to see "Priscilla" every week until it finishes at the end of the year


), and has been taking hers with her each time so she can watch videos on the train.
Apple doesn't release figures breaking down the sales per model, so I don't know how it is split out there overall, but most people I know with them in real life and on forums have the WiFi only model, and the few that have the 3G model wish they'd not bothered spending the extra £100. Why? Because a lot people find they really don't need it that much. WiFi at home, work, hotels, coffee shops, pubs, McDonald's, etc. etc. For the odd time there's no WiFi, and if you can't tether to your phone, there's still a tonne of things you can do with it, it isn't just for browsing.