Having worked in the maritime industry all my life, I feel for those sailors that are missing and their families.
At the time of the incident, a vessel I am involved with was / is working in the Gulf of Thailand and was waiting on weather, they were reporting swells of 5 - 6m and winds peaking at close to 50NM per hour.
Hopefully there will be a thorough investigation in to what went wrong, to sink a vessel of this nature is not as easy as some on this thread think.
From what we are hearing on the grapevine the initial cause was a loss of propulsion for whatever reason, which led to the ship getting beam on to the seas causing her to roll violently (she had a narrow beam), from this water was taken on causing the eventual sinking.
In heavy weather all vessel Masters will point the bow directly in to the weather, this is the only way to safely navigate rough seas.
Since Titanic, all ships are made of watertight compartments, flood one and the vessel will not sink, inclination tests are also done to determine how many degrees of list is the point of no return, again, a compartment can flood and not cause the ship to capsize. This is especially true of Naval ships for damage stability / control.
It is possible that one of the watertight doors below the waterline was open and the flooding was in more than one compartment, until the investigation it is only speculation.
One poster mentioned free surface effect, this can be a very bad situation for a ship, however, if all of the freeing ports are doing their job it should not cause a vessel to sink.
Let's hope the missing guys are found safe.