A lot of people keep saying that only a few Uchiha ever unlocked it, but, that seemed to be more of a deal during peace time, I mean, in Madara's time many if not most Uchiha seemed to have it, and Itachi even implies that killing friends for Mangekyo was somewhat common for the clan (which would require many to have not only gained sharingan, but also trained it to its full potential). Honestly, it doesn't seem like it was really out of the ordinary for an Uchiha to gain the sharingan.