Here is the link to a Seattle WA automotive technicians website that will explain almost everything to you. I'm specifically including the link about the 2010+ Outback Legacys but you can read all his other blogs and articles while you're there.
Subaru Changed Their Head Gasket For The 2010 2.5L - Seattle Subaru Repair
Here is a video explanation of the 2010 as well.
YouTube - Subaru Owner Tips: Subaru Changed the Head Gasket for the 2010 Outback
He gives full explanations on what is causing the problem and he even helped give a couple design queues on the MLS gasket they use for older models that has yet to fail on him. The Turbos and H6's have been using MLS gaskets for years with much lower failure ratios. So having a MLS or "beefy" gasket is the first plus the semi closed deck keeps the block from flexing as much which rubs the gaskets. Metal moves and thats just how it is but a semi closed deck block moves less so there is our second plus.
I never book marked the PDF I found that had the full Subaru PNs but the new gaskets end in 670 and the old ones were 633. The current turbo gaskets are now 770. I found a comment somewhere where this was acknowledged but no one new what the 770 update is.
I'm a backyard mechanic but not a certified one. I hope I've helped point others in the right direction. If you have a mechanical question about this search the blogs on all wheel drives website and if you don't see your answer just ask him. Hes a really nice guy who knows his stuff. Hopefully this will put current owners with concerns at ease, like myself, and help prospective buyers buy with confidence.