in some phones you can set the usb port to work as usb mass storage device and not as mtp, this depends on the manufacturer, if it what left that option or not, check in the phone settings
this phone as many other phones are using the usb port as mtp protocol only, so the system sees it as a camera and lets you download the images only
this has nothing to do with the os, this was intentional so only that content can be read and not written
you can use airdroid with your phone to upload and download any files to it just by opening firefox and writing a address the app gives you
for samsung phones there is a app called samsung kies wireless but i never used it so i ignore what it does and how it works