Well, I'm basing it on the actual gameplay trailer, which shows actual gameplay, and my 5 years of experience in computers and 11 years experience of gaming.
Of course, we will never know for sure until it is released. Its not really speculation or rumours, I'm basing it on what the gameplay trailer showed us.
I'm just trying to give people a good idea on what the specs are expected to be for skyrim.
"Based on a trailer" is speculation and rumors. Firstly, it's running on console, secondly, it's a compressed internet video, and thirdly we know nothing about the scenario that was filmed in.
While I'm sure 5 years of experience (That's almost as long as skyrim has been in development for!) count for something, they do not give you magical powers to tell how much power a game will need from orchestrated compressed footage of a console game.
However, I suspect your speculation will be accurate, simply because every console port from the last few years has required about the same amount of power and skyrim does not look to be changing this.