Originally posted by LikeASong:U2 and many other artists have been doing that for DECADES. In the case of U2, they started declaring all/most shows as "sold out" (regardless of the number of tickets sold) in 2001 if memory serves. Since then, virtually all of their shows are marked as "sold out" in Billboard and similar sites, whether they sold every single seat in the house or there were literally thousands of tickets still available to purchase on the morning of the gig.
It's a fact, it's not debatable.