OK, Nielsen is doing away with the pageview because of all the AJAX and Flash and RSS and everything else that lets users aggregate or interact with content without generating a page for that content producer's Web site.
Is the ad industry happy about this? I don't konw, but I will check. I do know that advertisers, or at least media buyers a) tend to be a little behind in getting technology and b) have relied on audited and machine-counted ad numbers in the digital realm, unlike the print and broadcast realm where they buy assertions based on surveys and statistical modeling and suppositions.
If Nielsen gives us some sort of metric for "engagement" such as repeat visits or time spent on site, that's more vague (and easier to spin as a positive) than the pageview metric. Publishers have been arguing this for years, and it's interesting that Nielsen is going along.
True, pageviews are easy to game - you can jack up your pageviews without serving more real content. Then, again, if someone's looking and sees and ad, they've seen the ad.