[mrweasel]

Even the solution in the article seems to suggest using cookies.

I don’t understand the problem, if people want to try or sign-up for your service they’ll locate the signup button. That’s a one time problem. A hidden login button just annoys existing customers.

My feeling is that this is down to testing without privacy in mind. Your site might be fine, but others aren’t so a minority of users will clear cookies at the end of each browser session. That’s not a senario most will test for or experience.