There is lots of coins on sell in TH, but not much dollars to buy them and in effect the prices are constantly lower there. It has been puzzling me why someone insists on selling on TH when he can in one hour move his BTCs to MtGox and sell them for a better price? A few hypotheses:
- it is a manipulation to keep BTC prices down (that was my initial thought - but I've seen it being bought entirely a few times - so that was not that cost free as one would think)
- it is a TH trick to attract more traffic to their site
- moving money out from MtGox is just too costly and complicated (for example for SEPA transfers they charge 2% - and the exchange rates for EURo used in these transfers are equally awful).
It could also be that quite a few people don't trust MtGox.