I have four thoughts:
[1] Mac OS X 10.0 was supposed to be in beta by Spring (2000) and shipping Summer (2000).
It arrived Saturday March 24th, 2001.
So this isn't a long delay in comparison.
[2] People who say most people care about iPod/iPhone are not wrong, but at the same time I feel Apple would be unwise not nor look after / aim to please the type of people who post on here, as we (at least most of us) are amongst their most loyal customers.
[3] Finally, the company only has a finite numbers of engineers. There are probably only a finite number of people in the world with the talent, skills, ability, desire, motivation etc. to work on these large projects like OS X for iPhone and Mac OS X Leopard.
Therefore I don't think it is totally inconceivable to believe they shifted resources from Leopard to iPhone.
[4] Delaying iPhone would only get it in the media again, which would be not
necessarily be the worst thing in the world. All adds to the hype. Mac OS X is a product which is already out, but is getting older and competitors are catching up (MS with vista, the Linux community with Ubuntu). Maybe there is a better case for resources to be allocated to it and not the iPhone. But we don't have all the details, and far more intelligent and experienced people than me probably made the decision anyway.
I'm disappointed, but life goes on.