Strange, it must indeed really depend on the person in charge or the availabilty! I still remember a couple of years ago I saw boards advertising upgrades from Economy to Dynasty for not so much money (it still wasn't much cheaper then the differnce between Dynasty and Economy I paid in advance so why take the risk) displayed at the Economy check-inn counter next to me. Don't rember if this was in AMS or BKK though but it could be both to!
In Jan 2004, D-class ticket was a Dynasty seat with more or less Economy-service but CI got so many complaints (not mine, I am not on a plane to eat and to me only the seat really matters) they changed it again to full Business-service. Passengers who paid Y-class were seated in 1st.

Wouldn't be to surprised if D-Class is offerd for extra €€€ at check-inn again this year. I booked my flights (9/1-3/2) somewhere in May already but my girlfriend only booked 2 weeks ago (9/1-27/1) and they still had plenty of availabilities in D-Class! They even sell it on the website now for 1299 euros for exactly the same dates! I've never seen this before, January is high-season or isn't it?