I think gurps hit the nail on the head. With the economy slowdown, and loans harder, more people are bailing on their reservation, and the dealers kept stuffing the orphans with add-ons but discovered too late that people don't want them.
Our dealer has (or had) about 7 orphans on the lot for weeks now, including ONE that was a Passion in the color combo we wanted... but, they stuffed the orphans with LoJack and GPS and chrome rims and whatnot. If that car had been offered to me, I'd have been driving a Smart for a month now and they'd have one less car on the lot.

I've read in other threads that some dealers are learning the lesson, and probably won't be stuffing them with options as much as they had been.
However, I don't think sales are slowing because the waitlist is still long and supply has not yet caught up with demand. Perhaps, at some point in mid- or late-2009, you might see some Smarts finally sitting on a dealer's lot for walk-up sale...