This is not exactly true. When Apple releases more powerful gadgets , newer apps will require "higher" specs . When you can not run apps from the app store, your iphone/ipad will be almost obsolete other than the ability to browse and make phone calls.(ok play music and videos too)
For example, Infinity Blade which was released in later 2010 will NOT run on original iPhone or iphone 3G, and I doubt the performance on a 3gs. Basically it only supported 1 generation back. That means soon we will same games unable to run on iPad 2 and needs a minimum of iPad 3.
On the other hand, guys who bought a ps3 in 2006 are still enjoying the latest releases for ps3 in 2012.
basically, the faster they upgrade the faster your iPad will not be supported, the more obsolete it will be.
it does get worse, because your iPad does not meet the minimum requirements any more