with custom tags how would you realistically incorporate all the choices into a few clickable filters ?
You don't get it because you're missing the point.
The ideas was NOT to try to incorporate
ALL of the choices... Only a few, good, commonly used ones. Sure, you could do all of it with panes and custom searches in the search box, and that's all fine and good if you want to find which picture, video, or song has a specific keyword or whatever...
However, consider this scenario:
You come back from a photo shoot, with 850 images. Download them and assign them all to a new "album" (which is how I categorize my projects in MC). Then you go through that album in thumbnail mode, assigning ratings, editing in Photoshop, and whatnot. Now, say you're 1/2-way through and you just want to quickly see all of the Ratings >= 3 stars (filter out the crap) to see how many good shots you have thus far, and to make sure your "standards" haven't drifted over time (mine often do -- I become a more and more harsh critic as I go)... Sure, you could use a search and type in the "code" manually, but in Lightroom it is mindnumbingly simple and intuitive and lightning quick.
It is just a feature that most "photo browser" focused applications have.... Quick, intuitive, icon-based filters. Not trying to be everything to everyone (that's the job of the search box and panes). Just trying to be most things for most people in an intuitive and eye-catching way.
Those are examples using photos as the "media type", but I could use the same thing with my Audio files and video files (especially if said AW auto-changed the displayed "quick filters" based on what media types were present in the current view).