Jonny,
Am I? They say you shouldn't believe everything you read, and I read this (arf arf!)
Thats why a Stop orders full name is a Stop MARKET order. If the order was converted to a Limit, you may not get a fill if the market follows through. This means the exchange would not be able to charge fees, ie they miss out on business. It is in the exchanges interest to generate as much liquidity as possible.
I think - and I may be wrong, that ALL exchanges take market orders for this reason - to make it easier and more attractive venue for people to trade at.
Does anyone else know?
Rognvald - I posted a couple of websites a few posts up. Both sites produce monthly news letters which are quite interesting. You can also try searching exchange websites it those deep dank, dark corners where no-one else goes!