People forget that Nokia feature phones ruled the mobile market for years on end, serving a particular type of customer, who may want to occasionally surf the web and use applications but primarily just for calls alone. This market has not changed. Low/mid-range Android phones have taken over the old feature phone market and brought new features. To these users, which still happen to be a majority, these phones already have a lot more features than previous devices and so the need for updates is not something that is a priority for these buyers.
Those more interested in the cutting edge, will no doubt have settled for an iPhone or a high end Android phone, as those devices are touted as flagships and are more likely to be updated and serve as mascots for their respective companies.
The reality is that there just isn't much of a business case for every Android phone to have updates to every single version. It's up to the OEMs to decide when to update based on their own individual business models. Apple only has one mobile device so its update process is undoubtedly going to be easier to manage, however, that being said, legacy Apple devices have seen atrocious support when being updated to new versions of iOS.
The bottom line is that those that want updates will seek them out, one way or another. Most new Android devices are on 4.x now, so eventually Gingerbread 2.3 will be displaced, but due to the nature of the Android model, this will take a bit of time to refresh, but I'm willing to bet that by this time next year, the 2.3 share will have been more than halved.
