Apple sells a lot more WiFi iPads than it does 3G iPads. Best data I could find on a quick google is admittedly almsot a year old, but:

90% of the tablets use WiFi only (some have inactivated cellular chipset) meaning that only 10% of the tablets (as of Q4 2011) were cellular activated. Operators who start to bundle multiple devices by single data plans and data buckets are going to see a better yield in this category. We expect family data plans to be introduced in the US market soon.

Source: http://www.chetansharma.com/USmarketupdate2011.htm

I don't mind this so much presuming it can do Bluetooth tethering with my phone [vs WiFi due to power usage issues]. If I'm the device's user, I'll likely have my phone with me, so having a redundant radio in the device doesn't add value. And, if I let someone else use the device while I'm not around, the likelihood is that there will be an available WiFi source.

I'd like it-just-works connectivity between my phone and any other devices I carry with me. Right now, I have to hit a couple buttons on both devices -- a pain for short-term usage scenarios.