This version is spec'd at 26 oz but I see...
This version is spec'd at 26 oz but I see it on the Patagonia site at 28 oz (not the 2013) but what must be the 2012. What version is the 26 oz here? Weight (v. warmth) matters!
The real question is what size they're giving you the specs for. Frequently they'll state "Specs are for size Medium" but depending on who it is they might state specs for a small or X-large.
I'm going to guess that the weight savings this year has to do with the change in fit. I had plenty of room in last year's SMALL to wears layers underneath, but this year's MEDIUM measures almost exactly the same as last year's small. The older DAS compresses smaller, but the newer DAS is likely to last longer. The Primaloft Synergy insulation is a CONTINUOUS FILAMENT insulation which is far less resistant to migration and loft loss after repeated compressions. It also is 'loftier' than Primaloft One and takes up more volume for the same warmth. That's why this year's DAS feels puffier. The big downside to this year's DAS is that it takes up more volume in your stuffsack. It won't compress as small. The upside is that the continuous filament Synergy won't lose loft with repeated compressions. Here, Primaloft is trying to go after Climashield. It shouldn't be long before you see Primaloft competing in the sleeping bag market where Climashield dominates. Even though it doesn't compress as small, continuous fiber is what is needed to avoid loss of loft and warmth over hundreds and hundreds of stuffing compressions.