It does... it offers both options. You just have to pick one

I brought this particular request up at our weekly meeting today. We'll be looking into a resolution in the future to make it easier for new vehicles to be added with less confusion. We'll also look into making it more straight forward for new members to catch on/understand how best to add/track their vehicle.

It'll likely be as simple as adding an option as "Starting Odometer" of the vehicle as soon as you add the vehicle to your garage and it'll be placed prior to your first fill-up.
Fuelly does do just that. We refer to it as Trip Mile tracking-
FAQ: What's the difference between tracking with Odometer vs. Trip Miles?

Is there an email list or something that lets users know when new functionality is added to the system?

Not at the moment. We've tossed around an idea of a Newsletter. We've used a mailing system in the past for our mobile users to let them know what's to come in regards to integration with Fuelly.com, so it's not out of the question.

We'll revisit that idea in the future. In the meantime, whenever we make any significant changes, it's usually in response to a post/thread here, and/or we'll start a new thread to let everyone know.

I agree with the OP. With new vehicles you should be allowed to enter 0 miles for the first fill up (like the new cars I have bought that come full after the dealer filled them prior to delivery). Just had this issue with a new Sonata I bought for my wife.

Fillup# 1
Gallons: ?
Miles Driven: 0
MPG: N/A

Fillup# 2
Gallons: 10
Miles Driven: 200
MPG: 20


What value is Fillup #1 actually offering you?

Exactly Robert, I've tried to explain that a "fuel up" is when you've already added fuel, driven a certain distance, then refuelled. That's a fuel up, not simply adding fuel.