I think the point is:
portfolio = "what did you do?", whereas
resume = "where did you work?"
If all your resume contains is a list of previous employers, that is a horrible resume!
Where/when you worked should be just a company name and a date. That's it. It should be followed by a very brief description of what you did there.
So OP's resume would contain something like:
- Lumera (2002-2006):
I was solely responsible for version 1.0 of the software and led the team that did version 2.0.
I think when Jeff Atwood says "portfolio" he means not just things you'd put on your resume, but source code and publicly available articles you've written, and for some reason a twitter account.
But not just "I developed that closed source project, over there." That's what everyone has on their resume.
-- Ninja Edit---
Actually I just looked at Jeff's other article, and apparently what he calls a "portfolio", is what I call a well written resume.