One of the reasons I can remember for this is that without the cut, feeds can get very large, to the point where LJ won't syndicate them anymore.

I wonder if there is a way that people can have their cake and eat it to in this instance. What if there was a way to say that you wanted the full feed by adding a parameter to the URL at the end?

That way, the default feed wouldn't get so huge, but unless someone explicitly blocked outputting a full feed, you'd still be able to get it.