(side note - there are two toaster/coffee machines)
It is trite to say that the mobile phone has become pervasive in modern society. The iPod has also become rather popular. Now - the problem with most converged devices is the sacrifices which have to be made; this is very obvious for the toaster/coffemaker - because there are virtually no shared components. The situation is different for a music playing mobile. Indeed, the only real barriers are price (and size, to a lesser extent); both devices share a need for a display, an input mechanism, storage space, and attractive design. Perhaps simplicity is a virtue, but surely the convenience of a converged device is sometimes preferable? Indeed, the Zeitgeist encourages convergence.
The has already occured twice to mobile phones. First it was converged with the PDA; second, it is about to be converged with digital cameras. The PDA convergence is virtually complete, at least for what used to be known as the Pocket PC. A wide range of devices now available from HTC makes it such that purchasing a PDA for daily use is easier if you also intend for it to be your phone - why carry two devices when a single device (of the same size/weight/shape) will do better? The situation is not as clear for digital cameras, because the picture quality from mobile phones is still lacking - but the intrinsic issue there is that carrying a camera around always was never as common as it is today, and it has arguably only become so common because of the availability of camera phones.
This issue is also likely to exist in the case of music players - not everyone carries one around - but what about the portion of the population which does? And indeed, something else Rubenstein said argues for convergence, using his criterion that a converged device should make things better. I quote: "The iPod is substantially more difficult to copy than that Walkman was. It contains a whole ecosystem of different elements, which coordinate with each other: hardware, software, and our iTunes Music store on the Internet."
Modern mobile phones have all this nice bandwidth (at least 144Kbps) lying around, searching for a purpose... and now imagine if you had the option of a subscription based, unlimited use music service...
The iPod hardware is a work of art, and it's software is incredibly easy to use - but wouldn't you trade (a little bit of) that off for a device with which you had immediate access to every song in the world, in the palm of your hand?