Before I joined Stack Overflow, the site was something that I just thought was just another resource on the Internet where I could come to find solutions to problems I was facing, solutions which were asked and answered by others.
I didn't join the community, until one day I saw an answer posted about Comet that helped me solve a problem I was searching for days to solve. Someone downvoted the answer, left a snide comment, and there it sat with a -1 score.
I really wanted to leave a comment defending the answer, and I really wanted to tip the scales and upvote the answer, but the Stack Overflow system denied both of my attempts to right this wrong.
Determined to fix this problem, I quickly started looking for a question or two that I could answer in order to earn the reputation score needed so I could leave my comment and upvote the answer. I had my first 20 reputation points in just a few minutes, left my comment, upvoted the answer, and then became addicted to answering questions on Stack Overflow.
In summary, if someone really really wants to do something on Stack Overflow bad enough, such as providing a great answer to an old, outdated, protected question, and that person is really passionate about the subject matter, then he or she will likely go get those first few upvotes and gain the necessary privileges to provide an answer to the question.
Now, I'm not sure if protecting these accepted questions is indeed the right answer, but I am almost certain that the 10 or 20 rep user that answers those first few questions didn't spend 10 minutes of their time gaining reputation, just so they can post spam on a protected question.
I hope this helps Stack Exchange make a good decision on whether or not to implement this.