This may come as a really big surprise to you, but I don't think they see the market quite the same way that you do...
Consider if you will that they just sold 20M units in Q42005 - there is probably no real sense in Cupertino (where corporate HQ is) that they are missing an important segment of the market. I don't have the numbers to back it up but my educated guess is that the adoption rate of the iPod for the first 5 years is ahead of the CD, the DVD and most certainly DVD-A, SACD and HD in household penetration.
Which might lead you to the conclusion that the hi end audiophile market is not a particularly rewarding one - especially since what it appears you really want is the same thing for less... BTW IMHO a 60Gb Nano without a screen would be pretty much useless
As Onhwy61 points out, Apple is going to continue to push the video angle because video capability is a key to a new revenue stream - downloaded video. First the iTunes store, next the iTV store though I am sure they will have a catchier name LOL
Yes they do change DACs - they did from the Gen4 (Photo) to the Gen5 (video) The real issue is not the quality of the DAC, its everything in the circuit that comes after it. If you haven't, you should use the line out from the dock not the headphone out - big difference. Don't know if this is any consolation to you but Steve Job is a perfectionist and he hangs out with a lot of cool people who know audio (Bono for one) - he will always put the best DAC he can in the device
I would guess that they are on a 3 or 4x per year introduction pace right now. They seem to be intent on leveraging their lead and fragmenting the market to make it ever harder for anyone to come in and gain a foothold - kind of a float like a butterfly strategy - I'm here, I'm there and you mr competitor don't have the marketing budget to be everywhere I am at once
One thing is for sure, its never dull
