On the one hand, this could be a simple and honest representation of market value, based on supply and demand. It is easier to manufacture blood than ink, after all; babies are really easy to make. However, we do not use humans primarily as a resource for blood, so although blood is technically easier to make than ink, it is much more difficult to harvest (When's the last time YOU gave blood?).
This brings us to the other hand, which is that printer companies don't make their printers specific to their ink cartridges by accident. And you know those deals where your new laptop comes with a free printer? That's not crazy, that's an investment that the printer company is making in you, in anticipation of all the lovely green you'll drop on their precious, proprietary black.
The future is, of course, digital, and as more and more people have smartphones and tablets and start adopting cloud storage services such as Google Drive and Dropbox there will be less and less need to have a “hard copy” of something. Universities (UT for one) are already using services like Blackboard, and, depending on the professor, a lot of assignments are being turned in online, and never going through the print stage at all. So people won't always need ink, but people will always need blood.
Well, maybe not always.