My boss got us smartphones back in the Windows CE days, because he's a huge geek like the rest of us. The problem was that while work was willing to pay for the phone part the data was WAAAAY too expensive so we didn't have that. Combine that with lackluster wifi availability and the fact that you had to manually turn it on and off because it drained battery out of range, and we didn't end up using the "smart" portion much. Not because it was too hard to use or any of that BS, but because there just wan't the ability.
Now, data is cheap, and my phone auto roams on and off of wifi, and work has complete wifi coverage. So I use my smartphone often for its "smart" features. It is always on data of some kind and like you, I never get near my cap, particularly because it is usually using wifi.
That is the biggest thing that changed and made smart phones useful to me, and others I know. It because affordable and practical to use the smart features. Data is something that is an included feature in most phone plans these days. $40/month can get you a line with some data.
Touchscreens and such weren't the thing that changed it for me. I still liked Blackberry's real keyboard + scrolly ball interface. It was having an affordable data plan plus a processor capable of handling the BS of the modern web.