Not having it reset ever wouldn't work in many cases, though.
Let's say I wanted to see all songs from Metallica's Load album. So I click Metallica and Load. Then I want to see Megadeth. So I click on Megadeth. They don't have a Load album. So now what? Should MC just assume I want to reset the Album pane in this instance?
There are some searches that are inherently hierarchial, and there are some that aren't. The problem is, even the ones that aren't inherently hierarchial can be, and we may want to perform one. By removing the hierarchial nature, you just made it more difficult for yourself.
By allowing a View Scheme default, either hierarchial or not, you can pretty intelligently decide that an Artist\Album View Scheme should be hierarchial, but a Year\People\Places\Events view scheme probably makes more sense not to be hierarchial.
And then adding in the alt-click override gives you that final bit of control.