Originally Posted by AssertnFailure
That is indeed an interesting point...one that I had never really thought of much myself...
However an ability should not have to be passed down for it to be qualified as a bloodlimit. Perhaps it may be a little over-analyzing, but it seemed Haku's mother did not expect Haku to inherit her bloodlimit, even though it was a bloodlimit. Even more credible, perhaps, is the point that not all uchihas are capable of unlocking the Sharingan. So even if your parents are both uchihas, you still might not inherit their abilities. Just as the shodaime Hokage's kids didn't inhert his ability.
You could even go farther to observe a more rapid mutation/evolution effect occuring with the chakra characteristics of decendents. This happens to such a degree that certain abilities might only exist within single generations, and then could immediately be lost again through dominant/recessive relationships between their abilities and the abilities of their spouses. Considering the immense variety of distinctly unique jutsus out there, this would pretty much have to be certain.
Finally, Sandaime Kazekage's iron jutsu is a characteristic of his own natural chakra. This is why Sasori is able to harness the ability just by possessing sandaime's body. If the body makes all the difference, then what else could it be than genetic?