Seems to work only with US to US flights. "LGA to ORD" works, "FRA to SIN" and "HAM to TXL" don't.
SFO-AKL has direct flights though. I know, I've done it. NZ8. Nice plane.
edit: Actually I checked and "sfo to akl" does in fact give me results.
Oh, and it's in a 100-seat all-business-class A340-500. I'm guessing they couldn't do it with a fully-laden economy section. Then again I'd hate to fly 19 hours nonstop in economy.