There will be tons of Apps for the iWatch that will be add supported. They are already being designed. Why would it be any different than the iPhone?? In fact I think it will be worse because instead of banner ads etc. because of screen real estate all the ad placements I've seen will pop up full screen for a bit.
Get used to it!
I don't think the marketeers are that stupid and do what you suggested. They don't want to piss people off because that would be counter productive. On the phone, you see a banner ads, and occasionally an annoying pop-up. But for the most part you can view your content. The ads takes up less than 10% of the screen.
I expect the same for the iWatch. Ads will most likely be a logo and at most a few words, like a haiku.