I'd feel it would be more accurate to move the shounen/shoujo ai and yaoi/yuri categories from demographics to genres. I understand that shounen is a demographic because it targets a specific age group of boys, the same goes for shoujo with a range of girls, shotacon is for shotacons, lolicon for lolicons, and things like josei/seinen are made for mature readers.....those are demographics because they have a distinguishable class of people they are aimed at. Whereas things like yaoi/yuri and shounen/shoujo ai do not always come with a set of people they are looking to attract. However, on occasion they are paired with a demographic - some yaoi are seinen and some josei. So changing those to genres would make adding series less confusing with the whole one demographic suggestion when a series is actually both a yuri and a shoujo.

I have get the feeling this was discussed a few months ago...

you could go through this section, it should be somewhere there, afaik the demographic only displays the magazine it was published in (like shounen jump) else the demographic there could cause problems with correct classification...
(that would be the reason, that most web-comics don't have demographics)

but I don't trust my memory --_--

ah here it is:
http://www.mangaupdates.com/showtopic.php?tid=34686

not really what this is about, but it contains some points...

sry ><

in need of romance?
uncommon, sad, sweet

There are no current plans to change any of the genres or demographics

A just ruler amongst tyrants