The rule has good intentions, but I don't think it was thought through very well. By my understanding, it was meant to protect players from the people calling in from home to report potential violations. But, as they said on the telecast, if the initial call didn't arrive until last evening, he would have been DQ'd. Because it was caught while still on the course, he gets 2 shots. So Tiger in some respects lucked out because of the people (fans) who the rule was meant to protect against.
On a semi-related note, this also could have been a huge disaster if Tiger was in the lead at, say -7. I would suspect that many of the players who would have missed the cut b/c of the 10 stroke rule would have left town last night. Getting in touch with them to return to the course would have been nearly impossible.