Sorry, you cannot expect me to believe that "enough is enough" and wait this long before you announce that Lance Armstrong will not contest the charges.
What it suspiciously sounds like is that the USADA had the goods on him, and after very careful examination of the evidence, Lance realized that the jig was up. They had him where they wanted him, with his samples, witnesses and positive tests.
The USADA is not stupid to risk its entire reputation, scarce as it is, going after him after previous attempts had failed. Unless of course, they had solid evidence. Otherwise it'd basically threaten their legitimacy if they went after a decorated, retired cyclist and were found wanting.
They charged him on June 13, 2012. Why did he wait ten weeks before realizing that "enough was enough?"
In time, Lance will be viewed as a doper, even if the sympathy today lies with him. A fighter does not give up because someone accuses him again, and certainly does not take ten weeks to take the high road. Besides, is he now going to spend his life defending himself? If he does, then "enough is enough" is a lie. If he does not... wait, anyone really believes that he won't deny that he doped? Of course he'll. Every chance he gets, thereby confirming himself as a liar.
"I had enough" is not going to go over well, if he spends any time saying "I had enough which is why I did not defend myself." It is self-contradictory.
I really want to be wrong on this one.