i guess the reasons are:
- design, design, design
- prinziple: the apps should not distract from the content and therefor go out of the way (funny thing with ical/address book...)
- "unified look" (e.g. that's why the buttons in mail lost their color)
what they forgot:
- color is one of the best informations to distinguish items (unless you're color blind, but then you would still see a difference in shade)
- the sidebar is to be used (and not like the buttons of safari that you absolutely don't need, unless you're my grandma and don't understand multitouch), therefor every information that is available helps using it
- the principles of human interface that were developed by Apple in the last century (bigger, colored icons are better - it's strange that the dock works with color and no text, while the sidebar now works only with text... talking about "unified look"?)
and I guess Apple won't listen, unless a huge amount of people send feedback.
well, why should they?
- they are absolutely successfull when they do what they want and don't listen to critics
- when a new OS is released many complain: hey they changed that, bring it back. (if there is no visual change, people complain: there is no change!)
- they are successfull, because they leave the past behind
- i can't find the quote, but i read something like: jobs told pro consumers (i think for final cut) that apple will drive the innovation and that apple won't be listening to what the pro users want
i just hope they bring back the color to the sidebar, because that was a change that is not user-friendly and unefficient. infact this is the main reason why i didn't buy lion yet and had my itunes sidebar fixed up with color.