All right, this does sound kinda Illuminati but I don't think the Magic market is reflective of actual supply/demand. If WOTC prints billions of cards for new sets, there are probably hundreds if not millions of each rare in circulation. However, TCGPlayer might only have 600 copies listed.
It's a lot harder to spike cards in new sets since stores often have backstock and a lot more people have the cards and might just decide to sell if the price goes up. However, for older rares and stuff that is legitimately hard to find (ahem, my Reserved List foil thread) it's not difficult to buy them out.
You'll also notice a pattern in regards to which cards keep their post-spike price and which ones slide back down. Obviously they'll never fully go all the way back down but you get the point. There's cards that shoot up and that becomes the new price (LOTV, SCM) and there's cards that shoot up and drop down immediately (Ghostway, Skaab Ruinator). Basically, it's a game of perception and information.
When LOTV goes from $40 to $80 (like it did a year ago), people rationalize it by saying "Modern is growing," "Jund is doing well," etc. because it's a proven card with results. When foil Skaab Ruinator shoots from $2 to $12, people say it's a "buyout" or "speculators" are behind it. Notice that for both LOTV and Skaab Ruinator, NOTHING changed in the aggregate supply. Both spikes were caused by stores and speculators. The difference is they got away with it with LOTV and didn't do so with Skaab Ruinator.
You might argue that since people are paying for LOTV and stuff at their post-spike prices that the spikes were simply price corrections. But remember something. Magic is a LUXURY and 99% of players don't have an in depth sense of Magic Finance. Therefore, it makes no difference whether a card is $40 or $80 if you can "justify" its price enough to the common crowd.
That leads into this sub. I think that it can cause real price movements as long as good enough justification is provided. However, you gotta be smart about your picks. There are dumb speculators and smart speculators. The dumb ones bought out BBE and foil Ruinators and the smart ones bought out foil Siege Rhinos and foil Lingering Souls, but in essence they're all the same- they're not really affecting the price; they're simply testing what players will accept. Which specs seem more "justifiable" to you?
tl;dr it's all a conspiracy mang.