Well, I say dodgy because they're mostly rejected panels from apples supply..
		
		
	 
No, these panels are not 'rejected' by anyone.  Please do not post things like this on internet fora unless you know what you are talking about.
Apple and co. simply purchase the A+ rated panels from LG at top dollar.  LG also has available other panels such as A and A- rated ones.  These are, understandably, cheaper.  LG does not send Apple a bunch of random panels and get sent back 'rejects.'  LG does prior in-house testing to see which batches fall into which category (A+, A, A- etc.) and price them accordingly.
That said, the price of a panel is also dictated by supply and demand of that particular panel type.  With so many 'Korean' monitors sold on eBay using A- panels, these once super-cheap panels are no longer quite so cheap, especially the pixel perfect ones.