See, that's where we differ. I find storage directly on the device non-essential, precisely because there are services such as Dropbox and SugarSync.
On the other hand, I find mobile Internet access
crucial. So the first two iPads I bought, were both WiFi+3G versions.
However, times are changing: iOS 5 introduced the ultra-easy and hassle-free, excellent "mobile WiFi hotspot"
feature -- so when I buy iPad mini with Retina display after it's released, it will be the 16 GB WiFi-only model. Why? Because it's so easy nowadays to use your iPhone's mobile Internet connection on your iPad as well, while on the go.