I barely use Adsense (it's only on one page that offers a fairly popular small freeware program) so I don't tend to worry about it too much however...
It seems to me that, in order for the contract to stand up to scrutiny in UK law, Google should, at the very least, inform you of the gross click income on your site as well as the amount you are paid. In the absence of this information, it is impossible to compare service providers, something which would normally be considered essential.
The surprise here is that no one has challenged this before now (and that Italy is the first to do so). If Microsoft and Yahoo were smart, they would jump in and publish the necessary information, thereby making Google look bad.