I was going to post a similar question, but was distracted with Petrino.
We just had a similar discussion in my league. I simply assumed that the rosters would lock this week on ESPN, but they didn't. And now, since it sets up a loser bracket for every team, technically, anyone can make roster moves. In our case, I initially posted a message that rosters were locked, but one guy complained, saying it wasn't in the rules. I had no choice but to agree, and ruled that playoff teams could make FA moves and non-playoff teams could, and I would deal with the rule specifically before next season. This is our first year in this league, and it's hosted on ESPN, which I'm new to.
My question is, what is the specific justification for locking playoff rosters? I now have one league that does, and one that doesn't.