A couple of things...
I'm not sure how much the average forum user is aware of the whole OGL vs D20 compliancy issue (though many are very aware, of course), particularly casual users. It really seems to me that most will instinctively view AU and Midnight as D&D products, whatever the technicalities. There certainly has been a lot of discussion of both in the Gen Discussion forum. Thus, putting discussion of such products may be confusing to some.
Also, I think it's worth noting that AU and Midnight are not stand-alone RPGs (as far as I understand), like the others normally discussed in the d20 system forum.
Well, anyway, whatever the moderators decide will be OK with me. I keep deciding to wait to buy AU,then I go to that long AU thread (now in the d20 System forum) and receive an urge to get it.