Just confirmed via CES that VZW has jumped on board.
When new Android devices come out you can purchase via Google Checkout. You will need a Google account as well.
No difference but it's just an option. It will be especially great for non customers who already have a Google checkout/Account...click click click.
All in one place to shop for your device and carrier. A lot of people are always wondering if they can get X device on Y carrier now they will know.
Honestly it shouldn't hurt Verizon. It actually could get them more customers if someone can click around on Google's site and see that "oh damn I was going to go to TMo because of the Nexus one but it looks like its on Verizon too!". Just another way for people to purchase a Verizon phone.
Also even if Google sells them, Verizon gets the monthly $$$$