I don't think it says anything about their solvency, insolvency would normally cause people to get their coins out asap which would have the opposite effect. The explanation that its the go to cash out place could hold but why all of a sudden ? Somethings definitely brewing, would have thought someone would be arbing the gap as its been pretty constant.
Lack of people's memory can be astounding sometimes... Bitstamp has been the "cashing out" exchange since time immemorial. It has also been "the bearish exchange" since, forever. "Bearstamp" is not a term coined recently.
You're right: it's interesting to wonder what causes the renewed selling pressure/"cashing out" event currently (maybe insider knowledge from Chinese traders? I don't expect it, but it's possible). But in either case, the price gap in the current form is not a problem at all: if you want to liquidate coins in volume and get your money out fast and reliably (and you don't mind a bit of KYC anal probing

Yeah, my point was more why all of a sudden the difference due to being the cash out place rather than why all of a sudden is it the cash out place. That then leads directly onto your second point

This suggests in the simplest explanation that for some reason over the last couple of days a largish amount of coins have been "cashed out". That is always interesting to speculate about. We all know as well that selling a large amount of coins != running off with the fiat never to return.