Money stuck in exchanges keeps the Bitcoin price artificially high. If Mt.Gox ever processes all withdrawals, more people will convert to fiat to get their money out. So prepare for a price drop when they do.
It might also increase trust in bitcoin and the ecosystem, which could lead to another run-up.
Mt. Gox is almost irrelevant to Bitcoin at this point. Since they're not paying out USD (at all) or EUR (much), and only an idiot would deposit there, most of the "volume" there has to be the same money sloshing back and forth within Mt. Gox.
Your illustration made me laugh. It's sad, but true. Last night I was chatting with a friend about this. And it dawned on me that it's like people are all excited about trading, but they can't get out. It's just like a bunch of rats racing around in circles inside an empty cage or something. It was so ridiculous, it made me laugh then too.
If you can't get fiat out of gox it is essentially like using a sample forex account where you play with funny money.
May as well be monopoly money.