Default Apps showing up then disappearing.

You guys notice some apps will be on the market, then the next day they are gone, then appear again in a few days? I noticed this with Linda File Manager, Hello AIM+, Meet Me, and a few others. Actually, Meet Me hasn't shown up yet.
Black HTC Dream running Ion -> Black HTC Magic running Cyan -> HTC RAPH100 running XANDROID -> Samsung SPH-M900 -> HTC Glacier running CM7.1RC1

Currently on Motorola Atrix, unlocked running Neutrino.