One of the main reasons for this is that most people work in sRGB which is a disastrously small coliur space AND which has quite a lot of CMYK colours that it can't reproduce.
Photoshop always goes over CieLAB mode to change from RGB to CMYK and vice-versa, but can't make what isn't there in the first place. What is needed is an RGB colourspace that covers the entire CMYK. Therefore it is adviseable to work in AdobeRGB1998 throughout if you work for print.
In PS 6, color management was still avoidable, in 7 no. And they're right about that. Once again, it is a fight against habits and inertia from people who "know their business, so why change?"
Besides: people tend to forget that no monitor can ever show CMYK: PS tries to give you an impression, nothing more. So with a well-calibrated monitor and good profiles for your scanner, monitor etc you can have an idea of what's coming. But to get a really good idea, you need a chromalin.
And then, finally, when all's perfect, the biggest problem gets on the stage: if it isn't the temperature, then it's the humidity, and if it is neither of these, it's the rubber blanket that's too old, or the ink that's a different brand, or...etc etc ad infinitum.
ahh, printers!!!!!
