Honestly, with only five iPad generations having been made available, each with differing release circumstances, this seems to be a very hokey claim to be making.
For instance, my first generation iPad was pretty much screwed out of updates to apps beginning in 2012 (two years after release) and was completely sluggish and barely able to do most of the things I had previously used it for by 2013. If I had the money in 2012, it would've been replaced in 2012 which is only two years following release.
Take the iPad 2 by comparison, it's not bleeding edge and it definitely shows its age, but it's still viable to use and it's now been out for three years. If I owned one, I probably could hold off buying an upgrade for at least another year (which would give it a lifespan of 4-5 years from release).
The third generation iPad will be different in that in terms of CPU, it's more or less the same as the iPad 2, but with double the RAM and graphics power, but the retina display evens it out. So really, it's an iPad 2 with a retina display, meaning that in terms of CPU power, they'll both probably become too slow around the same time, meaning, and generally speaking, the iPad 2 and third generation iPad will both be ripe for replacement around the same time.
The fourth generation iPad will probably have more time being "fast enough" than the third and probably around the same time as the iPad 2 has had given that it is a natural evolution forward in every under-the-hood way from both the iPad 2 and the third generation iPad. It's still too early to tell, but it looks likely that the current iPad Air will follow suit in kind.
The first iPad mini was already a year and a half behind in performance in using the CPU from the iPad 2 and not one comparable to the CPU of the contemporary iPad and iPhone. Now with the second generation iPad mini using a CPU comparable to that of the iPad Air and iPhone 5s, both of which are considered "current" and "recent", owners will probably find that iPad lasts them considerably longer than the first generation which left the gate already behind.
Where most find a need to replace an iOS device because it's either too slow, can't run modern versions of apps, or both, ultimately it's all relative.
