I grant you that Exchange support will push the device into the enterprise, and likely act as a trojan for other Apple products in that segment, making it crucially important. However, Apple's current bread and butter is the consumer market and Apple will ignore it to their own peril. Providing a simple to use and elegant consumer syncing solution would be a great addition. It would sell more .mac accounts for $99 and quiet the legions of people that complain about .mac now. And imagine if they offered it for the PC? You wouldn't get all the cool iLife tie-ins, but they could milk a lot of PC users for $99 just to get syncing and they would be constantly enticed to switch to a mac to make full use of .mac.
At any rate, I'm just happy they seem ready to add the service. Exchange and .mac syncing are not mutually exclusive. They will have to come up with a nifty way of keeping contacts and events segregated though so that you aren't syncing personal stuff with work stuff. Not a crucial separation for some people, but for many I imagine it will be. Most people use their work-provided Blackberries for work, but as Apple attempts to unify the device world so that people only need one for business and pleasure, they will have to make the interface between the two obviously segregated, but easily navigable.