cost vs. benefit
The key is to make the cost greater than the benefit, or at least make the two close enough that spammers can find "better" ways to get benefits. You can achieve that by increasing the cost (eliminating the means by which spammers offload their resource costs on unsuspecting MS Windows users, et cetera), decreasing the benefit (eliminating most of the return on investment spammers get, such as by getting everyone to stop responding to spam), or both.
Even phishing requires a balance of cost and benefit that favors the phisher sufficiently to make it worthwhile. The benefit is just less prone to reduction by user education than plain ol' unsolicited commercial email.
