Typo in article, it's Samsung M9T not MT9.
So, Samsung's M9T 2TB laptop drive is only 9.5mm thick, which is the standard thickness for laptop drives. But has 3 platters. So why didn't Toshiba make their 3TB laptop drive be 12.5mm thick? that should be enough for 4 platters, since, the industry has shifted 1 platter laptop drives from 7mm thick to 5mm thick. 2 platter drives from 9.5mm thick to 7mm thick, and 3 platter drive from being 12.5mm thick to now 9.5mm thick (like the Samsung M9T).
Also, Seagate must be using 5 platters to get 4TB in a 2.5" drive, yet their drive is 15mm thick too, indicating further that Toshiba could have put it in the 12.5mm form factor, so it could be used in some laptops, like the Asus G50VT and others and also the optical bay of laptops with the hard drive caddy.
The 2TB M9T is slightly less than $100 to buy, might as well get that.