The rate of spam to a form is roughly constant over time, whereas the rate of spam to a published email address goes up over time as the site is repeatedly scanned by spam robots and the address added to more and more spammer lists. While spam detection is good, it isn't perfect. As your total volume of spam goes up, so does the amount that sneaks through the filters. Additionally, at a certain point it becomes impossible to look in your spam filter for misclassified real email. Eventually you're overwhelmed and have to change emails. If you're going to publish an email address you have to consider it a burnable resource that you will replace once the volume of spam is too high.

If the author hasn't experienced this, I think it must be because they haven't done the exercise of leaving a live email address on a public website for years.