Actually for number 3, assuming you're talking about the mini usb and the square type USB, I'd say the miniusb is better for smaller gadgets. So it wouldn't be ideal to put a regular USB size connector on all types of gadgets.
Ipod's dock connector is wide so it can physically stand the ipod, iphone, or whatever up when plugged in. So the physical design of connectors often serve purposes other than just to transmit data. And for this reason we'll probably always have proprietary connectors.
You didn't mention micro-usb. I have within one meter of me, devices that require USB type A ("regular"), USB type B ("square"), mini USB, micro USB and an iPhone.
I've got various Card readers, HDDs, Hubs, etc. that take Mini-USB B, but I've never seen Mini-USB A or any of the micro ones in the wild. Apparently Micro USB will be used for charging mobile phones henceforth.
Ipod's dock connector is wide so it can physically stand the ipod, iphone, or whatever up when plugged in. So the physical design of connectors often serve purposes other than just to transmit data. And for this reason we'll probably always have proprietary connectors.