That's par for the course for workstations, it's not an Apple-specific thing.
Taking a look at Dell's T7600 workstation, upping to 32GB of 1600MHz memory is $720, adding a 256MB SSD is $1000, adding a 2TB HDD is $600, adding a second Quadro 5000 video card is $2165.
Well, they did update the Mac Pro, it's just a really weak update that still doesn't make it worth buying.
Well Dell is also behind Alienware, similarly overpriced.