Companies like the goodwill they get from existing customers when they support products for a while, but in the end it doesn't get them much. Fact is, if OEMs keep updating older devices with new versions of Android it is more likely those customers won't buy another gadget any time soon. That's the churn that OEMs depend on to keep sales hopping.
Another side of the update coin for OEMs is the support costs. It is not cheap to get the new version of Android ready to put on an existing handset, nor to start supporting that version going forward. It is like taking on an entirely new support system for each version of the OS, and that is surely expensive.
Like all customers I want my gadgets to have the latest and greatest version of Android, to feel like I am getting my money's worth. I own a Galaxy Tab and I certainly wish it was getting Android 4.0, but Samsung says that is not going to happen. I don't like the decision, but I understand it from a cost standpoint.
Many mainstream consumers don't follow this stuff, and probably aren't even aware of the new version of Android, much less want to get it. For those more tech-savvy, don't overlook the outstanding homebrew community that probably has Android 4.0 coming to a device near you. My Nexus S 4G is slated to get Android 4.0 at some point, but I have already put a custom ROM on my handset from the homebrew crew. Not that I recommend that avenue for everyone, but if it's a big deal to you, wink, wink.
Image credit: Flickr user abulhussain