I just hate the cookie only tracking anyway, too many cookie cleaners out there. It really depends on the site, but in general I don't see a reason why an affiliate shouldn't be credited for all sales from the account of a customer he referred.
Sure, can be alot, but would the merchant make any money from the customer without me sending the guy there ? No, not a single buck.
Realistic ? No, but I expect more effort to track a sale than just a cookie only. I care less if it lasts 45 days or 90 days or whatever, but cookie only sales tracking is certainly not the state of art. There are more ways and they aren't rocket science.