I just got another Inside-Adsense Group post in my email; usually they are useless But today they were explaining the role that the "referral URL" plays in the adsense ad serving:

<email quote removed>

So the key words for which you rank on the SERPs will have an impact on the ads that are being served. This is pretty similar as saying that the "keyword topic" of your page will influence the ads you are served (it's contextual ads after all) but it isn't exactly the same for all cases. For example, you're page could rank high for certain keywords that aren't really on your page, maybe because of the heavy inbound linking using that keyword.

Also, a quick mention on what I will call the "stickiness" of the referral URL:

<email quote removed>

[edited by: incrediBILL at 5:13 pm (utc) on Feb 11, 2010]
[edit reason] no email quotes, paraphrase only, see TOS #9 , [webmasterworld.com...] [/edit]