By maintaining the 2.5 inch form factor, they make it easier for PC manufacturers to offer an option of either HDD or SSD in what is otherwise the same PC. Then the customer can decide the economic tradeoff between cost and speed based on individual needs.
"The unit is available in capacities up to 512-Gbyte and comes with a 6-Gbyte per second SATA interface and it comes in a 2.5-inches form-factor but at only 9.5-mm or 7-mm deep. "
I am not sure why they stick to this 2.5inch formfactor for SSDs, when they can make it really much smaller. Because of the form factor, ultra thin laptops like macbook air, directly uses a smaller PCB with a few flash chips sticked on it. And this reduces the upgrade options for the notebook.