you are correct. it is a design flaw in the optical block (it is heat related). if you replace it the new optical block will do the same thing eventually.
there is a class action suit in which sony has been made to extend the warranty period on certain models. this they have done at least twice.
if your model is part of the lawsuit (lots of links on web) and you are under the original or extended warranty periods, all sony can (will?) do is replace the optical block.
i have a sony kds60a2000 and am on my third optical block and the warranty extension period on this tv runs out at the end of this month, tv is 3 1/2 years old.
after the extended warranty periods however, sony customer service is not bound by the lawsuit and has more flexibility.
i don't know if your model is specifically included in the suit, but this appears to be what is occurring.
sounds like a very reasonable deal to me.