SirPrimalform: From what I remember, they're not robots, they're organic androids*. They're not human (in the strictest sense) but they're derived from humans genetically. They look human because that's what they started with, they worked on human DNA.
*android means an artificial human, it says nothing about whether they're mechanical or biological just that they're man-like. Robot on the other hand implies a certain mechanical nature, but says nothing about the shape (so it could be humanoid or like a robot in a car factory).
Yeah, that whole robot/organism thing is one of the mistakes in the movie that never got corrected. The opening crawl calls the replicants "robots" right before referring to their creators as "genetic engineers". From there on out there is not a single reference to them having any mechanical parts. It's always "genetic design", "genetic engineering" and the whole discussion between Tyrell and Roy only touches on biological issues, altering DNA, viruses, etc. Their eyes are clearly organic and we see Roy injuring himself to get a surge of adrenaline to keep himself going when his body starts to shut down. Everything we ever see in the movie clearly shows the replicants as organic beings rather than mechanical entities.
It might be meant as the Tyrell corporation moving on from robots to genetic design, but it's still weirdly phrased and only manages to throw everybody off...