If enough of the population is using devices that don't render flash, eventually, the advertisers will cave.
Very unlikely to happen in the next couple of years. Less than 5% of computers out there have Safari installed, and only 2% of total browser use is Safari (so imagine how little is represented by Safari Mobile).
The fact is that us Mac and iPhone/iPod Touch users are a tiny minority in the web universe. Only advertisers dazzled by shiny objects flock to the iPhone - and they soon become disillusioned by the tiny universe.
From my own personal experience, my company has developed a rather cool new way to view magazines on computer screens that we'll be launching soon. It's browser based and way better than anything currently available - it's actually quite magical The iPad is an ideal machine for it, but the numbers of users will be so low, even if the iPad is a 'huge' success, that if we want to reach a large audience (which we need to do if we're going to make any money out of it) we're better off building it in Flash. We'll probably do an HTML5 version eventually, but not for a year or so because the browsers with the greatest penetration levels (IE for example) don't support large chunks of HTML5. And who knows what might come down the line in the next 12 months. I suspect Adobe may get their act together and tighten up Flash which would knock HTML5 on the head beacuse there are a lot more Flash developers than HTML5 developers.