Probably the box where this didn't come up was cookied. Which works on one's own computer, but public computers can be another story (OK that one was in my father's apartment). It was usually when I was in college, and was sometimes at the comps in the computer labs I ran into the, oh I forgot to delete the cache. And those lab computers usually were set to run with an inordinately large browser cache, measuring in the multiple GB range
And yeah, an option for temp vs permanent cookies could work also, if the user could be prompted so as to set their own computer different from someone elses...