On May 13, 2009, In iPhone Development, By Graham F
Apple announced that all applications submitted to the iTunes App Store must work on both 2.2.1 and 3.0, in order to make it through the submission process. If you application doesn’t work on V3.0 it won’t go up for sale. It’s as black and white as that!!
However, you can’t create V2.2.1 versions in V3.0 Xcode, [...]