This is curious. I'm sensing a divide between explicitly stating for the reader "why law?" and showing an aptitude for challenge and writing and critical thinking.
I think one of the reason pre-law advisors don't emphasize "why law" for the PS is because a great deal of recent undergrads who apply directly to law school may not have much that is concrete to discuss. Trying to create a "why law" essay out of a few marginally related experiences would likely result in an unnecessarily weak essay. Also, I have heard adcomms note that often what a pre-1L thinks their law path will be is so warped from the reality of law school that there is no point in writing a whole essay of what essentially amounts to rabid speculation. (All those trendy 1L books reiterate this point--that law school is never as one imagines it will be.) Though, if an application asks for a 'why law' response, it should be touched upon, I agree. Though, I muse that this prompt is really to weed out the rabid speculators. ;-)
I would argue that it is valid to discuss a topic that shows one's ability to surmount challenge--starting a business, doing something significant for the community, overcoming a large obstacle with grace and vigor--that may not directly relate to the law. Indeed, the strong, holistic essays I've seen have subject matter that is handily extrapolated to indicate an aptitude for great challenge. I've seen a number of strong essays this season, and a few standouts. I'd say overall that 50% of the essays I've read accomplish what they ought to--leaving the reader with a strong, positive, action-oriented impression of the candidate (bonus points for extreme memorability/genuinely unique topic).
Getting multiple opinions on one's essay from a source such as this (as opposed to a writing center or a professor) will probably result in multiple opinions, some of which are divergent. At this point in our education, I imagine we're pretty good at figuring out what advice 'sticks'--so you take what you need from what you get, I suppose. I wouldn't dissuade anyone from putting forth their honest opinions here (especially those that volunteer their time), but it is worth noting that the essay writer will have to contextualize the opinions they get. The onus is on the writer in this instance--the readers here all have varied experience with editing and feedback--that's just how it is. To ask for "comments one can use," then, isn't asking for anything concrete--the reader gives what they can, and you take what you need. Discard what you do not.
The edict "be nice?" I suppose I've had that trained out of me during workshopping, so I may be guilty of a somewhat surly aside at times.

But, I also keep in mind that we value personal feelings and self esteem to a great degree more in the US educational system than is asked for in most other countries. This could be to our detriment--I've heard arguments on both sides (some claim we learn more when we feel positive, and some claim we assume we've learned something if we 'feel good' about it). Suffice to say, one can say "gee, this isn't making much sense to me--maybe you should rephrase?" or "Man, this sucks" and the information is essentially the same--something in that section simply isn't working for that particular reader. The writer just has to interpret around the personality of the individual readers to divine the needed information.
glad to see the discussion alive and well! I hope this thread has helped a few folks during this nutty process.
~Dani