I think plenty of folks consider it and don't feel like it's worth the extra cost. And for folks w/ smartphones or laptops w/ constant internet access, it's probably not worth it.
I paid the extra because I tested out the K3G browser and found out I can snag my gmail, get maps, and check my toodledo when I'm on the road, and I don't have to have my laptop along to do it.
And the best part is--doing all of that works, but it's just enough of a pain that I don't spend much time online. I can get offline quickly and either get to work or get to reading. Using my laptop for those purposes often results in me "losing" large chunks of time. (Technically, I turned my laptop on about an hour ago to check my e-mail, but an Adidas ad caught my attention and then some Failblog videos and then a news story and then here I am surfing MobileRead!
)
We're heading to Canada in a couple of weeks, and I'm looking forward to leaving my laptop behind and reading a ton, but it's nice to know I can do a quick check for urgent messages while I'm sitting by a Great Lake.