Why doesn't Adsense kick over and display a non-Flash based ad when the browser doesn't support Flash? Google and publishers alike are losing revenue from anybody using an iPhone, Windows Phone and Symbian devices because the browser just doesn't display the ads when Flash is involved. These devices are also the way everybody's going, so the lost revenue is likely to keep growing.
Mobile ads aren't a solution either as these phones are now capable of displaying full versions of web pages.
-Tox