All the 30-pin connectors plug in just fine. What doesn't work is the ability to sync and/or charge through all these connectors as Apple changed the HW in their iDevices over time as the need arose. Again, it's a change in the devices, not choosing a new plug paradigm for each new device type or model. This is unprecedented in CE.
One day, we'll get Thunderbolt access to out iDevices, likely at much slower speeds though faster than USB 3.0. I wouldn't be surprised for Apple to make a new dock connector to make it smaller and thinner for the next decade of devices.
Great - they plug in yet they don't work. Now THAT makes a lot of sense.
BTW - have you ever heard of an earphone jack?