What's happening is basically the TARDISodes again. Back in 2006, each episode of Season 2 was accompanied by a 1-2 minute webisode on the official BBC site that teased that week's story; they also had some deal with a cellphone company that allowed them to be uploaded to people's mobiles in the UK. Most were stand-alone gags or what-have-you, and the one for "Girl in the Fireplace" actually gave one of the major games away right off the top. But the one for "School Reunion" featured Mickey and actually filled in a major plot hole in showing exactly how and why the Doctor and Rose ended up at that school.
Unfortunately BBC Video decided not to include them on the DVD release.
Now the BBC apparently has produced at least 3 such "TARDISodes" for Series 6, though they're calling them "prequels" this time around. Unfortunately, one major change since 2006 is that people outside the UK can no longer view video content on the official DW website, so it remains to be seen if the BBC will put these on its official international YouTube channel (like they did with the Comic Relief mini-episode) or if that'll be left to BBC America and the other broadcasters, and there's no way to predict if these will later turn up on the DVD/Blu-ray release, though the track record for BBC Video/2 Entertain releasing website-based content suggests more unlikely than likely.
Of course, if they are geolocked on the BBC site, they'll end up on YouTube within a couple minutes so I'm not concerned about not seeing them from here in Canada.
Alex