If the employer doesn't offer you a contract with terms about mutual notice periods, I don't think it would be prudent to unilaterally extend a lengthy notice period with no assurances from the other side. As the article admits, if you give six weeks' notice and the boss reacts angrily, he/she can turn around and fire you instantly with no notice, since the company never committed to any notice period. It's a completely asymmetric situation there. Giving notice closer to when you plan to leave the job (say, the traditional two weeks) reduces your downside exposure to loss of income.
I do think it would be nice, for both sides, if mutual notice periods of at least a few weeks became more common terms in employment contracts. That way the company can plan for the loss of the employee, and employees who are to be terminated can plan for the loss of job/income.
If you want to leave a company and burn the relationships you formed while you were there, then by all means, give as little notice as possible.