PPC schemes (such as Google Adwords) do build link popularity and are counted in the so-called "organic" Google index. Its counted in two ways:

• Google is crawling JavaScript links on Web sites. These outbound links are, it seems, handled by Google just like any other outbound link. Google's Ad-Words uses JavaScript for links.
• In the cached pages: The Google robot does store pages with their own PPC ad-campaigns on them. The outbound ad links at the moment of being gathered are used by Google in their link analysis. The in-bound text in the advertisement which produced the ad with the link on a page will, in turn, effect the ranking of the link. The selection of costly words (and inclusion on highly ranked sites) will drive (and this can be shown) up ranking and visibility.