That is just one of the realities of onboard systems. They'll always be new features in the next model year and there often isn't an easy upgrade path.
That's true of a lot of other gizmos we buy in our lives. For example, Motorola came out with the Droid 4 only a few months after I purchased my Droid 3. They also announced they would not update to the new versions of Android. So, I'm stuck in contract on a phone that is behind the times.
Of course, the big diff between iDrive and my phone is that iDrive is a far more significant commitment in terms of $.
That may change down the road as the philosophy that companies might move with is having hardware be less of an issue and the main component be upgrades via software.
My way of looking at this is that there is a big difference between "not having the latest features" and "obsolete." Look it like the six speed AT. Sure, the newer trannys have more speeds, offer better fuel economy, etc. However, that doesn't mean the AT in your current vehicle no longer functions or does what you need.