From a developer standpoint, the Major version releases are far more important. All I have to choose is "am I going to support 3.1.x devices, or am I going to limit myself to 4.x devices". Even better, now that iOS5 has arrived with (very pleasantly smooth) support for the 3GS, the choice is "do I support 3.x or 5.x" since the last years of devices ALL support the APIs in the most recent OS. That is huge.
Just yesterday I realized that a long-standing bug is fixed by iOS5, and that since nearly all of our customers will be running 3GS or newer hardware, I can depend on that fix with confidence when we release our next version soon.