Latent sales and website testing

I think a lot of people will and should do website testing, courtesy of the free Website Optimizer.

One thing I cannot quite wrap my head around is why the website optimizer experiment cookie only has a life span of 30 minutes. In other words, if you come to a landing page that has an experiment running and then leave or do nothing on the site for 31 minutes, your analytics would count this as a new visit and similarly you may see a different variation of the experiment.

Because many sales occur only after multiple visits – i.e. latent sales – it would seem to me to be more logical to show the same variation of experiment to the same visitor.

Perhaps this does not matter in practice as both short and long lasting experiment cookies may lead to the same conclusions? In any case, I still wonder why this approach was chosen.