I was active on ELU for quite awhile, even before ELL was conceived. 

As I look back on some of my ELU answers now, I realize: even then, many of those answers were really helping English learners (like when I earned a Good Answer badge for explaining the difference between [sitting **on** a chair][1] vs. [sitting **in** a chair][1], for example.)

I'm an educator by vocation and calling, not a linguist or etymologist. Now that there are two Stack Exchange sites devoted to English, I feel more at home in the one where I can explain those seemingly basic nuances of our language (like prepositions and definite articles) to those who can so aptly show us how complex and vexing they really can be.

As for this sentiment:

> a site for non-native speakers learning English

I think what's implied is:

> a site for native speakers to help non-native speakers learning English

Without the natives sharing their expertise, this site couldn't be as useful to the learner.

  [1]: http://english.stackexchange.com/questions/72831/sit-in-a-chair-vs-sit-on-a-chair/72836#72836