Why are the sprites and the general art together in the first place? Sprites aren't usually considered 'serious' art at all, are they? It'd be like mashing separate Fanfiction and Original Fiction forums together and expecting it all to work without a hitch. Or pokemon roleplaying and original roleplaying forums together and expecting the same thing.
Oh, wait.
...how is fanfiction posted online honestly less "serious" than original fiction posted online? :/ Neither is going to get published; both are practice-writing by amateurs; the only possible argument for separating them is that some original fiction has the potential to be published in some heavily edited form at some vague later point in the future, but even that is only because of copyright law and not because there is any actual difference between the art forms. For role-playing, where none has the chance of being published, there is absolutely no possible reason to make a distinction between that which involves Pokémon and that which does not. Fundamentally, there is absolutely no difference in any artistic sense between a work of fiction that involves species created by Game Freak and species created by evolution. To think one is automatically better than the other, or that one being relevant to one's interest does not to some degree imply the other might be as well, is nothing but senseless elitism. At least sprites and general artwork are distinguishable by something other than the arbitrary creator of parts of their subject matter.
Making the sprite forum independent of the main art forum would be a very simple matter, though honestly, if somebody is interested in seeing when you've updated your thread, why in the world would they rely on happening to see it in the "Last post" column on the main page? If I want to see when an artist updates their thread, I'll check the actual art forum regularly; I can't really see this dramatically affecting the odds that people will notice when you update, since the only way it'll attract more people is if they think the title of your thread sounds particularly interesting and happen to walk in when your particular thread is the last one posted in. But whatever floats your boat; if you want to try it, that's fine by me.
While we're at it (and I'm sure much of the spriters would agree) is there any chance of having a subforum for requests instead of them being together with ordinary threads?
Sure, can be done.
The actual art forum has some degree of genuine talent; the spriting forum is a bunch of children who think they're cool because they know how to use MS Paint. Were I an artist who frequently posted there, I would be upset, too.
Oh, come on. I'm not commenting on the quality of the sprites that happen to be posted in this forum, but I'm sick of people thinking they're cool because they say spriting inherently requires no effort. There is little to no effort in standard recoloring, yes; very little in your average thrown-together splice; but you can also make an art out of blending parts properly and scratching in between to make something that looks like a natural whole, and that can easily take a lot of time and effort. Pixel-overs done properly take hours, and scratch sprites are in no way inferior to larger drawings.
If you're going to protest with "But when they're working from other people's artwork, it's not as good as proper original art!": I would have absolutely nothing against an art thread where somebody, say, created digital art imitating photos or famous paintings, or photomanips, or whatever. It can be well done or it can be badly done, and it can be done with effort or with little effort, but denying that doing it well takes quite a bit of effort on the artist's part is silly. As long as the original artwork is attributed and not used in violation of the original artist's terms for its usage, I don't see why a person working from other material can't have their work recognized as well.
As for why scratch sprites are categorized with sprite edits and not other artwork, that would be because of sensible overlap of interests. People who make scratch sprites are more likely to also do other kinds of sprite work than drawing, and in critiquing a scratch sprite, there are all sorts of considerations that apply to pixel art in general but not to traditional art, while those aspects that apply to both traditional art and scratch sprites (anatomy and shape, coloring and shading, etc.) generally apply to some degree to at least some kinds of derivative sprite work as well.
EDIT: Sprite forum split, request shop forum made. I moved all the sprite shops on the first page of the sprite forum over; if you want me to move yours, or if you don't want yours to be a shop, feel free to PM me.
(Jesus Christ, I think there was one or two showcases on that page. o_O)