Your chances of getting ICS on your legacy device are virtually zero. whereas getting IOS 6 on the iphone 4S is assured.
There are two kinds of Android users in this world - those who care about this issue, and those who don't. The former tend to be the innovators and early adopters who pay attention to every new OS release and whatnot, the latter are the mainstream users who just want a working phone and don't follow the tech rags and don't really care about the details.
So what I wonder is, if you're in the former group, why buy any Android phone other than a Nexus variant straight from Google, which is the only one guaranteed to get the latest greatest OS updates as painlessly as possible? I'm in that group, and I couldn't imagine buying some mangled, bloated carrier-modified version of Android. Is it just the marginally better hardware specs that attract people?