I totally agree with you, a business as smart as apple doesn't seem like they'd release a brand new imac when their brand new operating system is right on the horizon.
What's probably happening is the new imacs will be officially announced on August 7th, for a release date of October __th when Leopard comes out.
It makes perfect sense. You buy the computer and then are forced to buy Leopard. Apple gets more money. Besides they can't wait any longer, June was waiting too long and they didn't release them.