Besides that it would slightly add to the price of the printer due to
the mechanics involved, they want to have you use up as much ink as
possible, because they make most of their money on the ink sales.
Older Epson printers used to have separate black and color inks and
cleaning systems. With the precision the heads have in terms of
positioning, they could easily have a small cleaning station which only
cleaned one area of the head (one set of nozzles). They could even have
a wet cleaning system which sued a cleaning fluid to wash the head area
down. To do this probably wouldn't add greatly to the costs, but it
would lower ink consumption considerably, and that's not what the inkjet
manufacturers are wishing to do.
Art
If you are interested in issues surrounding e-waste,
I invite you to enter the discussion at my blog:
http://e-trashtalk.spaces.live.com/