Why does the FIDE rating table go beyond 400? The FIDE rating regulations say:

8.5 Determining the rating change for a rated player
8.51 For each game played against a rated player, determine the difference in rating between the player and his opponent, D. [...]
8.54 A difference in rating of more than 400 points shall be counted for rating purposes as though it were a difference of 400 points.
8.55
(a) Use table 8.1(b) to determine the player’s score probability PD [...]

But table 8.1b (which seems to be used only for this purpose) contains entries that go higher than 400. What use are those entries? Why are they there in the first place if they cannot be used?
Why are they there in the first place if they cannot be used?


They were there in the first place because they were used. The 400 point rule came later.


  What use are those entries?


They provide interesting historical context which makes it easier to answer questions like this.

Perhaps a better question would be, why are they still there, or why weren't they removed when the 400 point rule was introduced. There are two obvious answers:


Inertia. It would take effort to remove them
Efficiency. If the 400 point rule is rescinded at some stage then the entries required are already there.