If you're interested only in learning about lower levels of the computer, and don't need to actually write at lower levels, it may be better to learn, say, MMIX.

But lots of people do need to learn C. They might not be working on hip new social web services, but they're out there.

In my work, I have observed recent computer science graduates filter in and get assigned to program embedded systems using C. Their knowledge of C was minimal. Their code tended to be suboptimal, or even bizarre to the point of, I wasn't sure why it compiled. I recommended they get a copy of K&R. They did. I don't think they got much out of it.

I don't blame them personally. They simply had not been taught C in school, and had never had a reason to learn it before. Trying to learn it on the job with antiquated books didn't seem to work very well. (Though some did eventually come to learn C well. Others migrated to different assignments not involving C.)

Whatever your reason for wanting to learn C, be it purely academic, or if you actually need to program with it, fresh, modern educational resources are a good thing.