Which sets are "core" and which sets are "expanded"? and why isn't this explained in the marketplace

Which sets are "core" and which sets are "expanded"? and why isn't this explained in the marketplace.


Basically I have no idea what would be in any of the packs/boxes in the marketplace besides bonds of war... which sets are core? which are expanded? is core just the original set? is core half the old sets? is expanded the other half? only some?

 

http://forums.poxnora.desertowlgames.com/index.php?threads/summary-nux-changes.193/

Under "Rune Sets"

So first expansion to 6th, 7th to now minus 1, and now

 

This makes core packs pretty awful and extended packs highly random but fairly good? seems like an odd way to divide things, but at least now I know!

 

There any explanation on why the split is where it is, and if they will eventually either move stuff from extended to core or split off a new 3rd set of expansions as we move along?

 

the old forum had a .... kinda answer. gedden (i think it was gedden) basically said that the grimlics descent was the line which was simplest to divide the expansions, citing reasons like ability complexity, core story info, and how rare/common runes were from the earlier sets to the later sets.... most of that is paraphrasing and depends on my notoriously vague memory, so no gaurantees. the core set therefore is a good starting place for new players to start thier collection.
he also said that as new expansions come out the "current" expansion would get folded into the extended set and the new expansion would be purchasable only through owl cash. this im pretty certain about.