Playing with the Grand Exchange database

From time to time I play a little "understand the Runescape market/mechanics" game with the Grand Exchange database. It's very simple, yet, I find it rather interesting and challenging.

Here is what I do:

• Open the list of Top 100 most traded items for 7, 30 or 90 days
• Start from the top and try to explain to why each item is there in the first place (whether it is due to some popular training method and, if yes, in which skill)
• Try to figure out why some items are higher than the others in the list.
• Try to find and explain patterns.
  

For instance, take Yew and Magic longbows. Those are the only non-stackable weapons in the list. Why are they in there? Of course, not because of a huge number of rangers, but because these bows are being high-alched for Magic training. So, those are in fact "commodity" items.
Or how would you explain huge gaps between raw and cooked lobsters (sharks, tuna) comparing to side by side positions of raw and cooked monkfish and swordfish? In my opinion it is a clear indication of lobsters, sharks and tuna being most common food items used in combat.

But there are a few items in there that puzzle me:

• Astral runes being on top of Law runes. Why? The only explanation I have is that Astral runes are used in Magic training (making planks) and Law runes are not (at least not anymore). Is that it?
• Presence of stripy feathers in the list. Who and why would buy them? How come they are on the market in such huge quantities?
• Most recently (in 7 days only) a presence of unfinished Spirit Weed potion. What is up with it? Why is it there out of a sudden?

Any ideas?