This is what the Technician that repaired my machine said happened, and by the way I went for a new Blue Ray drive not replacing the BR controller board and laser that had been burnt out, and I went with a local computer hacker shop.
This guy said the newer slims have a Blue Ray drive that is able to spin and read at a faster rate, more speed and faster reading because of the complaints to Sony about poor frame rates and lagging visuals for your games, Sony tweaked the Blue Ray for better performance unaware it would cause catastrophic over heating of the older Phat consoles causing the controller boards to burn out, most service shops just replace the controller board and the laser in a matching set, it has been noted that these repairs only last a short while (usually die shortly after the warranty expires) because it is still the same slower drive some will even try to replace the heat sinks but even this will not last, so I elected to replace the whole drive with a new one and I had them wipe my EPROM and install the firmware before 3.15, so now my PS3 is X Moded and I do not trust Sony with any further firmware updates if a game requires a update to play it I take it back to the store and get a refund, you can do this within 7 days at Game Stop, then I get the same game but in XBox 360 format.
No matter what Sony tells you this is their fault!
In a World filled with Lies and Deciet!
Telling the truth can be a Revolutionary Act!