OK so this is the original (rather old) post where I've got this from:
http://www.holidaypirates.com/holida...-553-eur639-up
It's a flight+hotel package, and basically if you select 4 people it only calculates the hotel for 2 people on some hotels (e.g. Ritz-Carlton NY), which results in a cheap price.
I checked this on Expedia.be and it gave me 6 nights in Ritz-Carlton + flights for 4 people for €980pp. Example dates: 30/12-05/01.
Not sure if this is worthwhile, and not sure what Expedia would do when you book this one though..
EDIT: My sample booking was from BRU. Link is fixed (thanks moseslin).