Love or hate Windows, one really good thing about Microsoft is that they support a Windows version forever. Well, not literally forever, but longer than the computer you bought it with is likely to last. Todays new generation computers, made up of smartphones and tablets, are not as lucky. One to two years is what you are likely to get.
Apple's original iPad, released in March 2010, came with iOS 4, was upgraded to for two years all the way to iOS 5.1. It wont be getting iOS 6 which will be rolling out to other iOS devices this September. The Google Nexus One launched in January 2010, started life with Eclair (Android 2.1) and moved on to Gingerbread (Android 2.3). It did not officially get Ice Cream Sandwich, released on October 2011. Basically, you can expect high end devices to get the latest OS for 18-months to 2-years. That does not sound all the impressive.
Many devices are less fortunate. The Samsung Galaxy Tab and HTC Desire HD, both released on October 2010, did not get official an official Ice Cream Sandwich (Android 4.0) updates from Samsung and HTC. Pretty much it got OS updates for just 12-months. Notably, these two devices are more powerful than several new Android phones and tablets which today come with Ice Cream Sandwich out of the box.
But Android is open source. This means, that someone else can legally build what the the Original Equipment Manufacturer does not. This month I upgraded a HTC Desire HD to Android 4.0.4 courtesy of the Blackout ICS Incredible ROM Blackout Team. The Samsung Galaxy Tab got Ice Cream Sandwich via CM9 form the CyanogenMod Team. These are stable ROM's which I now use as my daily drivers and based on months of test versions being released. This illustrates the power of open source. Two obsolete devices are now good for use for another year. And it does not end there. Jelly Bean (Android 4.1) ROM's for both devices have been on beta tests for over a month now.