After I started using LS (recently) I downloaded quite few themes and I ONLY took recent ones (those that came first in the lists sorted by date). That is something very sensible for a LS-newbie to do.

Now I can without further research name 4 themes using xPC, and only one of those NLMs it. (so 75% non-NLM)

This is of course only a problem for LS-newbies. Unfortunately even if you load a theme that NLMs xPC, you are still not out of the woods, because, as xanmolbjerg explained, many themes, even recent ones (see above) expect xPC in the LS-rootdir.

At that point even the doc-reading newbie has had it. He knows he already has xPC, and he would also explicitely have to know that NLM-ing xPC is NOT enough, but xPC ALSO has to put in the rootdir.

I really know what I am doing and I had real longtime trouble getting that clear.

So, yes: xPC must for the time-being be in the LS-rootdir because otherwise any newbie will be maneuvered into a really absurd situation, even if he reads every doc on the market (Nobody does that of course. Normally you try a few themes, find a large part non-working, and do the one reasonable thing: put LS back where you found it and forget really fast.)