For sake of this discussion PTP is MTP.
JA in your description of "safely remove blah blah blah" you are describing attributes of UMS / MSC.
Drives mount under USB Mass Storage Class.
Amongst the many characteristics of this is that many operating systems cache writes to UMS devices. This means that even through a piece of software may appear to be finished with the drive, and even though said piece of software may itself believe it is finished with the drive, the operating system will not have actually performed the write which had been requested of it. This means if one were to physically remove the USB device that the filesystem can be in an inconsistent state where the table of contents (FAT) need not actually represent what is found in the pages of the book.
I know I erroneously referred to MTP (Media Transfer Protocol, which is an extension of PTP (Picture Transfer Protocol)) earlier in the thread. My bad, a misthought on my part. For sake of this discussion they are the same thing.
PTP differs from UMS in that UMS gives the operating system full control of the memory card at a block level, meaning the operating system is responsible for 100% of the low-level treatment of the card. This can lead to problems as I described (when using a non-journaled file system.)
With PTP the camera itself remains in control of the memory card, and acts as a warehouse worker serving the operating system. Windows says to the camera "Delete file 1234" and the camera says "Ok, will do boss". The beauty of this system is that if the USB cable gets pulled at anytime during the conversation the camera either hasn't received an order, or the camera is busy performing the order and uninterupted by the pulled cable.
Contrast to UMS where the operating system itself does all the work. The USB cable in this example is like the umbilical cord attaching an old deep-sea diver to the boat (Windows) above. If at any time during the diver's work the umbilical is broken tasks will be left incomplete, and without records. This is filesystem corruption.