Have they actually made significant changes to address the rust issue? Perhaps that could be the reason for lack of avertisement. Either that, or they simply don't want to admit there was an issue for liability reasons? Whatever the case, I am sure this has as much to do with the dwindling sales figures for the last several months as being "outdated". Shame too, because it's probably the only reservation I have with any Mazda product. I'm sure most Miata's are put away in the winter, so probably the reason for their continued success.
From a legal perspective, it's not admitting liability to extend the duration of a warranty - it would be to market and say "We had a problem, but we fixed it."
Simply stating "Now with 12 year Rust Perforation Warranty" does not admit any liability - in fact, matching competitors' warranties is a very, very good idea. You want to show your product is reliable? Target the competitors with the better warranties. Until your reputation is one of bulletproof reliability, shorter warranties will scare off would-be buyers. That's how Toyota gets away with only 6 years.
It seems to me that the rust issue was band-aided. Wherein there was an issue about moisture getting into a crease in the rear wheel well, they installed foam to seal it - they didn't galvanize, they didn't laser weld, etc. VW does both of those things, and that's why their products don't rust after 3-6 years. Still, ze Germans need to swap their sensor suppliers before I'd ever drop my cash into one - oxygen sensors seem to always be culprit and about $1,000+ to repair/replace...but this isn't a German quality bashing thread).
The Mazda 3 looks the part (front license plate placement exempted) on the outside, the interior is following Merc and BMW (but that's not a bad thing, whether I like the pop-on screen or not), and their products are fun to drive and fuel efficient. I think better marketing will go a long, long way to growing the brand and its reputation.
"Reputation takes a lifetime [or in this case decades of corporate actions] to build, but only seconds to destroy."