I think what UI customization shows us is that software vendors providing customize-ability correlates with a lack of confidence in the defaults they ship. When someone creating software has a strong opinion about the "right" way, they can't see the possibility that anyone would ever have legit disagreement with their brilliance so they take away control. And when they can't figure out the right solution to something…
My conclusion: whenever the core product is done, the company will sell you the 'make it your own' pitch, because that's the easiest path.