It seems that many places require a 3 or 4 night stay with requirements for specific check-in days. I'm guessing it takes 'status' to be able to book single night reservations.
Actually, it is usually a 2-night minimum unless it is prime season, in which case it is 3-nights that begin or end on a weekend (for these purposes, Sunday counts as weekend). Within 90 days, this restriction is relaxed. Also, inside of 90 days you may be able to pick up a single night as the only restriction seems to be that you can't take one night out of a 2-night reservation; as long as you leave at leave 2 nights, you can take one night, and you can always take 2 or more (as long as it's not a split reservation and a portion of the reservation "splits a doublet") as noted above.
Confusing enough?
Status has nothing to do with booking flexibility.
What can be frustrating is you'll see availability that "should" be bookable - for example, you're looking for 3 nights starting on a Friday, and when you look, your desired Friday is green, meaning there is availability. But when you go to book it, the system returns the message it doesn't comply with requirements. The reason is the 3 nights are a split reservation and booking it would actually take out 1 night of a doublet.