[RjQoLCOSwiIKfpm]

I would guess the reason the cheaper ones don't have it is that making it removable implies making it accessible from the outside which implies adding a pump and hoses to pump the ink into it:

The slot for the box at my printer is at the back of it, not at the ink head, so the ink can only get there by pumping it.

(Not defending Epson's design choices here, just trying to explain them.)