Maybe much more complex
It looks a bit more complex that Apple have actually said, and Apple have not been smart in dispelling the confusion.
There is a lot of talk about the loss of audio line level out, and the Apple web page says that iPod out is not supported on the adaptors, leading many to assume they mean no line level audio out. Which it seems isn't the case. IPod out is a mode where an iPhone or iPod Touch will emulate an iPod in a manner that allows really nice integration into car audio systems, where it actually displays an iPod control screen, complete with album art on the in-car system. It is this that doesn't work. Assuming they are actually supporting line level audio out in the adaptor, the adaptors at least include a DAC, so it isn't just a connector. The adaptor probably contains more than this too.
The iDevices have never supported S/PDIF, and I very much doubt they will start now. Those docks that do support it have licensed a special USB chip from Apple that allows access to the internal digital audio stream. I doubt Apple will be giving up that control.
I suspect we are going to see some later technical descriptions abut the Lightning interface, but Apple have let slip a few things, and a look at some of the issues with USB make these make more sense. Apple say it is an 8 signal interface. Which is already interesting. USB 2 is two signal (+ and - signal) and USB 3 adds four more (superspeed TX +/- and RX +/-). The remaining two signals may be Apple simply keeping the old serial interface, or they may have done something much more interesting and the Lightning interface may not be USB at all, and the adaptor contains a USB interface chip as well as a DAC.
The plug is double sided, and I think everyone has assumed that because it can be inserted either way up it means that although it has16 physical pins, they are simply 8 electrical pins duplicated. This may not be true. If the socket has only 8 pins, sure, but if the socket has 16 pins we may see some slick use of differential signalling and symmetry allowing four pairs of differential signalling pins, plus the power, ground, and maybe power output for accessories. Apple have explicitly said 8 signal pins - so the question of where power and ground come from needs answering anyway.
Apple will want to future proof this for some time, so a range of things are possible. In a decade's time our expectations of what can be done on the connection interface, and indeed what we expect from our smart pocket device may be significantly more extended than we imagine now. Indeed, have a look at Thunderbolt. Cut out the two low speed signalling lines and a few redundant ground pins and it would fit. Who knows? The name is tantalising.