They clearly still retain ownership of the domain, and there are plenty of people out there (relatively speaking, within the WoT world) who still remember wotmania. It would be utterly foolish of Dragonmount not to use the wotmania domain to drive traffic to their site, even if it did nothing more than re-direct to the homepage without mentioning wotmania at all.

As it is though, an error page? What? I don't believe it. My guess is that they intended to leave the letter to wotmania refugees up for a year, and then do something different. That "something different" either hasn't been implemented yet, or they never bothered to check if their change went into effect (they may have set it up to change automatically, and just assumed it would work).

In any case, seems like an email to the Dragonmount fellas would clear this up quickly.

EDIT: It appears from a link on their homepage that they moved to a new site design / technical format a week ago. My guess is that the update broke the wotmania link.

EDIT2: They have a bug report forum, if someone with a DM account feels like letting them know the link is broken. I'm far too lazy to register myself.