I don't see why they shouldn't offer both. Buying the Nexus One without a subsidy would be the preference of some people since you don't have to renew your contract. I just wonder if Google and Verizon couldn't come to an agreement on things.
The Incredible supposedly has better multitouch support than the Nexus One.
I'm sure once its unlocked and custom ROMs can be made for it, there won't be much of a difference. Google is at least supporting older devices officially more than Microsoft ever did (or at least the hardware manufacturers are). The Nexus One might get official updates faster but since the Incredible is a new device, HTC should be willing to update it to the next few versions of Android.
As of now, I don't believe there's a way to turn off SenseUI. I prefer the stock Android homescreens with widgets over Sense. I'm sure custom ROMs will change that though.
Wrote up a quick article for the homepage too:
http://www.ppcgeeks.com/2010/04/26/n...ne-on-verizon/