More transparency concerning "Missing xmlns attribute for element html" or [VE][no-xmlns]

The website I've checked is
http://myallegro.ca/

This website, and others I've built earlier, used to validate sucessfully using the w3 validator. However, now I get this message :

"Missing xmlns attribute for element html. 
    The value should be: http://www.w3.org/1999/xhtml"

What I find frustrating is that I've already checked this website months ago, and this error wasn't mentioned, even though it was already an error (I guess!).

It would very helpful to add some kind of explanation about this change: is it related to a version change, new specifications, a bug in the validator?

The Markup Validation Service is a great tool, very helpful for web developers (I've learned a lot using it), and it encourages everybody to apply the specifications, but what I'm trying to say is:
the referee can surely change the rules as he wishes, but if he doesn't fell like justifying it, the players should at least be informed about the new rules ;-)

Thank you,
Mudar Noufal

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