Scanning for a small set of ports, as well as having a large time gap between scans is also a measure to avoid being blocked by IDS. The idea is being stealth, isnt it? You may need some more effort to get info, but you make sure it wont bring much attention.
A small number of connections to a few ports from different locations and at different periods sounds like a better measure than using fake packets, that might easily be spot as such. But sure, It doesn't resume all situations, so I stand that stealth scan has its uses.