I doubt it has anything to do with a measure of satisfaction and more to do with the 360 being the dominant console in North America, where games are generally cheapest, game vendors are more plentiful, and, frankly, you have a lot of overweight kids who stay indoors more often.
The last one might sound silly, but I'm pretty sure that the US is the most obese country in the world on a consistent basis. Contrast the leading position of console gaming in the US with Japan, a nation with a low obesity rate and where mobile gaming reigns supreme.
Honestly, all the consoles are similar enough that the satisfaction rate is probably nearly identical (if you leave out RRoD statistics). Any console that wins the core market in NA will probably have the highest tie-in ratio.
Now, as for this line, "I think the 720 will be the highest selling console next gen because the people who bought X360 this gen will continue to support the Xbox brand", I really don't see any reason to assume that. The 360 had a year's jump on the other consoles, but it's going to finish with the smallest installed base and by far the lowest sales rate. Right now, even with the launch of Kinect, the 360 is seeing a more pronounced drop than the PS3, which means customer interest is falling off at a greater rate--surprising, as Kinect was expected by many, including myself, to reinvigorate the console for a much longer period. It makes you wonder how the 360 would be doing if the Kinect had never been launched.
Globally, Xbox is still the weaker brand, as we see by that lower sales rate, and Microsoft has the most negative image of the three. In Microsoft's favor is their plan to unify everything under one umbrella, with "Xbox" services across a ton of devices. However, this will only be really effective if products like Windows Phone and Surface catch on at a high rate. I'm not sure they will.
Honestly, as I've said before, you can't predict how a generation will go based on a previous generation. People will gravitate toward what they see as the best product, even if it means breaking brand loyalty. That being said, Microsoft, which had the weakest hardware performance despite launching the 360 first, won't be launching first this time, which could hurt the growth of the brand.
I see next gen having a virtual three-way tie. It's going to be up to the console makers themselves to come up with something that can break that tie.