D is generally a discounted business fare (oneworld explorer tickets and the like). A bit misleading of them to use that code on a 'coach' fare.
As for the 'space available at the airport' catch - that's just dreadful! If you're planning on doing the Guayaquil run, be especially wary. I have never seen that run less than 100% full in business.
This is one cheeky promotion, LanChile.
[This message has been edited by OWdevotee (edited 11-27-2001).]