I think Apple chose to discount the refurbished Wi-Fi models more than the Wi-Fi + 3G models because most people, I think, would opt for the Wi-Fi only option and the deeper discount adds an extra incentive to purchase.
I think that the iPad 2 will retain the current 6 model lineup (3 Wi-Fi, 3 Wi-Fi + 3G) because Apple can still make more money on the people who want both. They'll probably think, "Why would we include an extra feature (3G capability, in this instance) that people would be willing to pay an extra $130 for?"
Just my opinions...