Agree with the rules, however the point of it is to book F for the long hauls, not J.how come? If you have one leg in F, and then the rest in J, you have to pay the full 420k which sux, but you can virtually do a RTW trip and visit a heap fo countries
Depending on your routing, you can get an F segment for no extra points cost (more or less) compared to booking segments separately. This is before you consider domestic J connections. Great value if you know what to book, which is great value nonetheless.
For discussion, see here:
Wiki - "oneworld" award (140K/280K/420K) Planning - The Definitive Thread