It's for convenience and practicality.
Every jack and plug has a maximum amount of cycles (how many times you can put it in and out before it stars to wear down inside.). Due to the frequency of use I put my rig through I knew that the jack on it that I plugged my HP's into would eventually wear down to be looser and provide a less secure fit. I can replace and reterminate my HP's any old day but it's more difficult and expensive to do the same for the E17 - I can't just do the plug, I have to buy a whole new amp. I plan on keeping my amp for a while so I permanently attached the R/A 3.5mm to the E17 which terminates into a female 3.5, effectively making the female jack the jack that gets repetitive wear, not the main one in the unit.
The other reason it's like that is because of my usage habits. I pull and put my rig in my pocket(or bag) upside-down, so that when I reach for it in my pocket, it's the right way up in my hand already. It also means my headphone cable doesn't need to bend in any way to sit in my pocket. So in conclusion, it's both a stress-relief (in two ways) and a repositioning of jack to make it more convenient to use on the go and in my pocket.
Ahh, I see, but nevertheless, very nice looking rig!