Why is image so grainy? In this day and age, we should have better images, even from 5.4 million kilometers away.
It's a few pixels across because it's not a telescope, it's a probe.
It's not about "this day and age", it's about designing something that can do a lot of science when it's close, instead of something that can do a fraction as much from farther away.
Even the best camera in the world would give you results that are pretty much the same.
If you want to ignore distance, then you should probably look at the entire frame of the camera. I'm sure it can take some wonderful snapshots of the stars that aren't grainy at all.
But if you zoom via cropping, your image quality goes away. That's not a failure of design in any way.
Perhaps we just need some kind of infographic? If the camera is a single pixel, how many pixels away is Pluto? What's the equivalent using (as one person suggested) a iPhone camera?
It's possible that single pixel wouldn't show up at all since it's pretty dim all the way out there, but Apple has been working hard on their low-light image capture :)
And that's of course not accounting for radiation protection, a very carefully designed CCD and mounting so you can actually do science with the results, calibration after riding up on a rocket, sensitivity across 350nm to 850nm, etc.
[1] http://pluto.jhuapl.edu/soc/Pluto-Encounter/view_obs.php?ima... (actually closer to 75-80 pixels across)