I think they need to curb this policy, or they'll end up promoting fragmentation across their devices. If iOS 6 is incompatible with the 1st gen iPad... or if many of iOS 6's new features are unavailable on the 1st gen... then you're facing fragmentation.
Also, I'm not sure how they can "sell" a first gen iPad over an iPad 2. "Well, this first-gen is thicker and less powerful, with less features compared to the iPad 2... and really looks antiquated compared to the New iPad... but hey, it's cheaper!"