The same applies all over Thailand, and not only to dive boats. The recent ferry sinking in Pattaya when all witnesses / passengers said the boat was grossly overcrowded (of course the owner said differently) The boat captain was found to have been drinking / taking drugs. Straight after the incident there was a lot of talk about what was going to happen in the future to prevent further such incidents, visits from government ministers etc etc. As usual, all their action was simply PR designed to deflect any bad publicity that may have a negative effect on tourist income, only a few weeks after this unfortunate incident the Pattaya authorities were proudly claiming a 100% marine safety record for 2013. Utter nonsense, there were several fatalities that I am aware in the area last year involving boats / jet ski's etc, apart from this tragic ferry sinking in November. Not surprisingly, nothing has changed and 3 months on everything is just as it was. Until the next time.
Simple facts are that firstly, the majority of boats in Thailand are not constructed to the same standards as they would be in western countries, many have been converted from their original purpose to cater for the more lucrative tourist industry, with such things as additional decks added without any consideration the alterations may have on the boats stability. Regulation on boat construction / operating standards / insurance requirements are not as onerous as we might be used to in the West. Enforcement of any regulation is sparse and fraught with corruption. Also many operators put profit first and have little or no regard for customer safety.
But it is Thailand, and despite what I Have said the vast majority of tourists that use boats here for what ever reason do so incident free. But the potential for marine accidents is still much greater than most of us would be used to in our own countries.