why is apple tinkering with plugs?

I'm really baffled by the fact that Apple changed the shape of the Magsafe power adapters ever so slightly in the newest line of Retina Macbook pros. The Magsafe power adapter, which is attached to the laptop with a magnet and comes out easily if yanked, is such a good idea that it's even patented.
However, in order to charge a new Macbook pros, you will need to drop $10 on an adapter, since the design has changed ever so slightly and the new sockets are incompatible with the old plugs. Granted, this component is very small and is cheap (especially compared to the $2000+ cost of the machine), but that's beside the point -- I don't want to have to carry around a little widget just to ensure that I'm able to charge my computer with existing chargers of mine.
What doesn't make sense to me is why Apple would change this now. One of the greatest things about the whole iPod/iPhone universe is that Apple has used the same exact USB cable plug to power and transfer information to its devices for years. This meant that even if you forgot your charger, chances are your friend would have one. I feel like the original Magsafes were just getting common enough that this friendly synergy began occurring, as friends and coworkers accumulated chargers from macbooks they have owned.
It's 2012, and this 9-year old 30 pin iPod connector is practically ubiquitous.
The decision to change adapters also isn't environmentally sound. Five years of selling Macbooks at a rate of 2.5 million per quarter means that there are at least 50 million of perfectly functional macbook chargers laying around that will become useless as a result of this design change. Soon they'll just be sitting in a landfill. John Biggs writes that Apple might be replacing the iPod connectors as well -- with an estimated 600 million of those around.
Perhaps Apple wanted to make some quick money by selling new adapters and chargers, or maybe new form factors and design constraints necessitate changes. But it all seems a bit fishy to me. I hope that Apple takes the opportunity to promote its recycling program heavily when shipping out these new chargers, or proves in a meaningful way the benefit of these new forms.