Uchiha is linked to Kyubi, they can control him through the Sharingan, it's a relationship apparently mentioned in secret clan texts and part of the source of the power behind the Mangekyou. At least that's what I gather from the Manga, they talk a lot about the nature of the clan and their abilities in chapters 385 to current(403).

I assume it would be because of Jiraya and the Third, both of whom would be expected to keep an eye over Naruto as one was Naruto's guardian and one was guardian of the Leaf, as such Naruto would be guaranteed to have a close relationship with the two people that the Fourth would be expected to have trusted the most.