1) When I look on a test account that's Plus, I see only two options greyed: "Someone removes me from their Friends list" and "Someone votes in a poll I posted". The actual wording of "I comment in someone's journal, on any entry" doesn't actually appear on the Notifications page, for the Plus or Paid account.
2) The wording is really confusing: it implies that if you don't have a paid account you still can check the box (untrue) but don't get notifications, and moreover it doesn't specify what notification you get. Is it a copy of your comment? A reply to your comment? A comment to the post you commented on?
3) The asterisk doesn't have a corresponding explanation anywhere, unless I'm missing something?