Yeah, I was thinking about this for several days now. Most new users right now are bitcoin buyers - not miners. Therefore the prices are driven way up, and people still prefer to buy 200 bitcoins for $6000 instead of spending time putting together a bitcoin rig for just $1500, which could more than pay for itself in a few months. We just might see the day when you can buy an awesome new computer for just 6 BTC, and the difficulty still manageable.