Actually it would hurt their iOS market greatly. iOS devices are worthless without their third party apps. And these apps can only be produced on a Mac. In fact, I bought my Mac so that I could build iOS apps. If not for 3rd party apps, it would simply boil down to the device, the software that Apple ships with and the browser. Android devices will clearly win hands down in such a scenario. Initially it would be the case of worse is better but over time it would overtake iOS devices in terms of features and sales.
iOS apps can only be produced on a Mac because that's how Apple wants it. In the unlikely event that Apple did decide to ditch the Mac, they'd port their iOS developer tools to another platform.
* Mac continues to evolve slowly, not have major innovations. Innovations that do occur will be on things that are aligned with iOS-like devices (like Launchpad, Mac App Store, Macbook Air's).
* Someday they will ditch Mac, when an iOS device can be used to (1) create new iOS apps, and (2) be a productivity machine (e.g. w/ keyboard / etc).
Those of us who like to poke under the hood will have to move back to Linux or something else.
