To use the example you helped me think of, why should I WB when I can colour balance? Or, why should use EV compensation when I can use 'brightness'?
(I pose these as rhetorical questions and food for thought)
Nikos, rhetorical or not, you've raised a couple of interesting examples, so I'll respond to them. Re the White Balance: find one of your images which seriously needs to be "white-balanced". Do it in Camera Raw using the white balance tools in the first section of the Basic Tab, render the image and save it as an RGB psd or tiff. Then go back to the raw file, undo the white balance you just created there, and render the file "non-balanced" into Photoshop. Then use whatever techniques you wish to use in Photoshop for correcting the colour balance. Compare the results on two dimensions: (i) perceived accuracy of rendition across the colour gamut, and (2) ease of workflow. I've tried this a number of times and Camera Raw always wins.
As for "EV compensation", there is a contradiction in terms here and a technical matter. Firstly, I assume we are talking at the stage of the scene capture, where EV is Equivalent Value - it trades-off shutter speed against aperture to maintain the equivalent exposure, so there is no such thing as "EV compensation". We do Compensation at capture time to change the exposure, altering the histogram. The technical fact is that we always want to get the best possible exposure at capture and rely less on Brightness or Exposure in either Camera Raw or Photoshop after the fact. The most usual example is the argument made for Expose To The Right (ETTR), also discussed extensively in these forums, and a correct recommendation. Under-exposures boosted in post-capture processing will usually display more noise than appropriate ETTR exposures which don't require such boosting.
In both your examples, doing the right thing at the right time is important, hence I believe the major reason for the interest underlying this discussion, and in both cases we find our answers with simple experiments and observation.