I could be wrong but I believe I read somewhere that tracks aren't "updated", meaning you can't just change a barrier or curb on an existing track, you have to download a whole new track. If that's the case, this won't be a "5 second update", it'll have to be a download of the entire Goodwood track again, but with the new changes. Not everyone has good internet access and they have a legitimate concern over continuously downloading what amounts to almost meaningless content in terms of gameplay.
That is correct, although Goodwood won't be too big. Maybe 80Mb or so.