The scene in which Fred asks Angelina to the Yule Ball made me wonder if there's a pattern to that kind of thing - that Fred is a touch more extrovert and outgoing than George. They do a lot together of course, but on the few occasions that one of them is described as doing something alone - there's also a moment earlier in the book when George talks about house elves with Hermione, for instance - there seems to be a bit of a difference in character. Of course, it's possible other people noticed this ages ago and that it isn't any news.