There are 216000BTC mined every 30 days (assuming steady six per hour rate), and the volume at Mt.Gox for the last 30 days is roughly 1000000BTC. Newly minted coins represent 20% of the market,
yes, at least 80 % of mtgox volume is the sum of early adopters selling, speculative trading operations and maybe there's room for fictional trades moving the market ; )
I don't think the price is tied to the difficulty.
+1