Now that former UFC heavyweight champion Brock Lesnar is battling his second go-round with diverticulitis, the UFC has to redo much of the imaging for UFC 131, to the extent the process ever got started. I found a video on YouTube that didn't come from the official UFC channel (and seemingly can't be found there), but looks to be the official trailer with the new Shane Carwin vs. Junior dos Santos headlining fight. You be the judge:
There is no "original" trailer featuring Lesnar. Typically the UFC releases them one at a time and usually during a UFC event. In other words, the first time you'll see a trailer for UFC 131 is during the UFC 130 pay-per-view broadcast.
But given that the UFC's top ppv star is now gone from the card and that UFC 130 and 131 are separated by a mere two weeks, the UFC has to be significantly more proactive to sell the 131 event.
The UFC appears to be selling this fight on the grounds that the main event features two hard-hitting heavyweights. I'm not sure there's much else to go on, frankly, but I have doubts about what sort of audience either of these fighters or their bout can pull even if all of it is compelling.