The reason Richard waited 20 years before revealing the precontract with Talbot's daughter Eleanor (and remember that precontracts were as binding as marriages) was that he hadn't been made aware of it. He was a decade junior to his brother, and while his loyalty to his elder brother was unquestioned and his service impeccable (after all, Edward did name him Protector of the Realm), Richard wasn't privy to all of Edward's amours. His information on the subject was not a fevered invention; it came from Robert Stillington, Bishop of Bath and Wells, certainly a reputable source.

The major problem, as I see it, with looking at Richard is that so many of the sources people cite come from the post-Ricardian, or pro-Tudor period; they are hardly unbiased. (More, writing in the reign of Henry VIII, states as fact that Richard was two years in the womb. It has been speculated that More was writing a satire, but I find this reaching a bit. Even the famous portraits, showing him as a hunchback, have been proven to have been tampered with at later dates, the height of the shoulder painted in and up to correlate with the idea of him as a monster.)

Even some of the primary sources, like the Paston letters and Mancini, are filled with hearsay. "It is said..." "It is believed..."

When Richard rode hard from the North and intercepted Edward V at Stony Stratford, he was acting correctly. Edward V was in the company of his Woodville uncle, Earl Rivers; he would not have even really known his father's family, since Richard was in the North for his brother, and Clarence was dead. You must remember that the Woodvilles were universally hated at the time, and mistrusted greatly. The Queen had a large family, and they married into many of the oldest families in the realm; it doesn't seem a stretch to me to think that Richard, most pious of his family, would have seen them as a pernicious influence on his brother, whose magnificence had turned to bloat under his sybaritic lifestyle, and would have thought it his duty to rescue his nephew from these people in his capacity as named Protector of the Realm.

Why did he take the crown? Did he truly believe that the children of Edward and Elizabeth were bastards, or did he, remembering the disastrous reign of Henry VI who had been a child when he became king, allow himself to be convinced? When you look at his character up to this point, and we have very strong evidence of his uprightness, loyalty, piety, decency and family feeling, it is hard to correlate that Richard with the picture of the evil uncle. It's even hard to do so with King John, and the evidence is far clearer in that case, in my opinion.

Unless you want to tell me that Richard developed a temporal lobe tumor, or some severe chemical imbalance, I find it hard to reconcile the portrait of the man from 1482-85 with the preceeding 30 years of his life.