Well, your definition is wrong therefor your argument is very flawed. The correct definition:
Obsolescence is the state of being which occurs when an object, service or practice is no longer wanted even though it may still be in good working order.
Hmm...
From Wikipedia:
Planned obsolescence or built-in obsolescence[1] in industrial design is a policy of planning or designing a product with a limited useful life, so it will become obsolete, that is, unfashionable or no longer functional after a certain period of time.
While you might argue that the iPad 3 became less fashionable once the iPad 4 came out, I think it'd be a hard sell.
Now, I don't argue that there isn't room to be irritated, but that irritation comes from assumptions about what Apple "owes" you. If you refinance your home mortgage and a month later the bank drops its lending rates by a full percentage point, which could have saved you tens of thousands of dollars if you had know, if you had waited, do you sue the bank? Nope.
Now, if the case is made that by their general practices Apple implied to their customers that iPads bought in, say, August would have a six month, or so, top market position, and because Apple then released a new version only a couple of months later, they effectively deceived their customers with those sales, then, well, perhaps. But if you look at Apple's releases, they have never been perfectly regular. Sometimes they release a minor bump shortly before a more significant update. Other times they let a release slide out a few months so they can release the full upgrade altogether.
If we were to take it from Apple's perspective. Suppose for a moment the following. The newest chip isn't ready yet. The new connector isn't ready yet. There is a desire to shift the release into the months leading up to the holiday season, to best capitalize on that consumer buying time. Competition is getting hotter all the time. So, now you have to make a decision, delay the new release completely for six months, letting the iPad 2 get longer and longer in the tooth while the competition is stepping up its game, or break the full upgrade into two pieces, the first being at the expected release time, the second being at Apple's desired new release time. Which of these approaches makes more sense, given the circumstances?
And, given that choice, do you tell people "oh, there'll be a new model coming in just a few months!"? Of course not. That kind of thing has been known to destroy companies before...