The 20th anniversary mac was to commemmorate 20 years since the birth of Apple. It was released in 1997. The time for a 25th anniversary mac has now come and gone.
This article is talking about something to commemmorate 20 years since the birth of the Macintosh. This would be due in early 2004.
As for the article, The only information they have is somebody claims that Apple has asked for some plastic enclosures similar to the Cube shells. I think it is unlikely that Apple will have a special mac to commemmorate 1984 - 2004, because lots of people will be saying
"hey, didn't they do that about 6 years ago?"
And they certainly couldn't call it the 20th Anniversary Macintosh.