Well, I thought the promotion part was being done by Samsung, not Verizon. And the 3G version cost more so...
The Non-3G version does not have a speaker/sound. You can only get sound by connecting it to a speaker/headset via Bluetooth. The 3G version does (obviously, it has to in order to be used for phone calls). The 3G version also has a GPS chip which the non-3G does not, and the slightly bigger battery to deal with more power usage from 3G - hence the slightly larger size.
Feature-wise, I wanted the 3G. Even went to a Verizon store (thinking we were getting the non-3G) and asked if I would be allowed to trade up to the 3G version, but they said no. But then, because my wrist really are on the small size, I was making my peace with not having those features but having a watch that would probably fit me better in the non-3G version.