David Pinto links to a pair of quotes from two sources on the issue of A-Rod giving signs.
Doug Glanville says there's no way Rodriguez could have gotten away with tipping opponents for so long without getting called out. He speculates Rodriguez was giving signs for his own team (something Orel Hershiser has confirmed), and crafty opponents were picking it up. Pinto says, and I agree, that it's likely a disgruntled former teammate probably took it the wrong way and told Roberts.
A player on condition of anonymity (Pinto guesses Jamie Moyer or Troy Glaus) told the St. Louis Post Dispatch he was aware of A-Rod giving away signs, and that he was very sloppy about it. He also says he was uncertain if it was to tip the opposing team or because he was just bad at being subtle.
My guess is this is a boring story tabloided out of proportion about Rodriguez just being bad at being in charge of pitch calling.