That sounds a little suspicious, doesn't it? And, indeed, it is suspicious. Here's the actual abstract:
First off, yes, the article _really is_ from 2000. I was surprised, too. Second, that study wasn't done in the US or the UK -- probably somewhere in the Netherlands, but could have been any of a half dozen western European countries. Third, the summary in Outside is inaccurate. The gain in "oxygen uptake" was not significant for the women commuters, only the men, and the frequency was not "only" three times a week, it was a mean of _more_ than three times a week. Finally, it is unclear from the abstract whether the cycle commuting was truly "low" intensity as Outside asserts; likely, it was moderate.
There are a wide variety of other problems with the article on bike commuting (not least of which is their idea of a good commuter bike -- the people running that study would probably have been appalled at what Outside was recommending, given what a typical commuter bike looks like in the countries in which the study was certainly done), as one would expect from Outside magazine.
On the other hand, at least Outside magazine took a break from pushing black diamond ski runs and other activities involving plane fare and crazy gear to write about something that active people could do in a down economy that might be both fun and healthful and not induce a lot of carbon emissions guilt.
ETA: To be fair, they did manage to engage in crazy -- both expensive crazy and stupidly inappropriate crazy -- gear in the bike commuting article.