At the time of this reply you've been downvoted a bit, and that is ridiculous.
No, not everyone requires certification to be a PM, but many places do, and in many cases it helps get past the resume filtering process.
So get a PMP cert if you want, or don't and find a company that isn't going to discriminate on the lack of a certification. It costs a bit of sanity and $500 some to pad PMI's coffers, but its basically paying $500 for your resume going to the top of the stack. Sucks, but it is how it is for a large enough number of companies to matter.
"Defacto" may be the wrong word, perhaps "ubiquitous" would be more correct, but your point is valid.
