Intuition and a quick google seem to call bullshit on this.
http://www.noxxic.com/gw2/getting-started/combat-roles
2nd link googled only to the wiki.
To further my point the wiki even states that while all classes can potentially fit each role, a person will still need to play that role. So basically, all classes, like in WoW, are similar to a druid or paladin in that they can potentially play the role of a tank, dps, or healer.
Now, if classes can fluidly switch between each role without needing a gear change would be a more proper question.