An article on ReadWriteWeb takes a look at how adopting HTML5 can prove beneficial for publishers and advertisers, specifically mobile display advertisers.
The heart of the article discusses how HTML5 on mobile devices is allowing for client side counting of ad impressions:
When desktop ad servers started using client side counting on the web back nearly 10 years ago, that made a huge difference in the confidence of an advertiser to believe in the new metrics they were receiving from digital advertising.
Client side counting allows for much greater accuracy when tracking impressions and, as the article points out, when ad-serving to desktop machines switched to client side counting it highlighted a 20% – 50% discrepancy compared to server side tracking.
Additionally the article highlights how HTML5′s ubiquitousness on mobile platforms (iOS and Android have support built-in and the tools available for agencies to create / edit their display advertisements presents a great opportunity to lower the cost of entry for creating advertisements, and reach out to mobile users.
Source: ReadWriteWeb — Forget Web Development, HTML5′s Biggest Impact is on Advertising