There's been a lot of speculation about DL drives fitting into the 15" MBP, with people questioning why a 15" can't have a DL drive, while the 17" (which is the same thickness) can. The 15" and the 17" are the same thickness, but that doesn't mean there is the same amount of room inside each, and doesn't mean that the 15" has the additional space that a DL drive requires.
Look at the keyboard placement on the 15" -- because the keyboard is recessed into the case, it intrudes on where the DL drive would have to go.
That's why the disc slot is about halfway up the front of the casing on the 15", but is at the top of the casing on the 17".
explanatory image (go ms paint):
Look at the keyboard placement on the 15" -- because the keyboard is recessed into the case, it intrudes on where the DL drive would have to go.
That's why the disc slot is about halfway up the front of the casing on the 15", but is at the top of the casing on the 17".
explanatory image (go ms paint):