maby he wants to price to go up, in which case generating only 10coins for a while would really move it up, but i do not think that a client would accept said block.
If I'm not mistaken, the rules only say that the reward can't be above the per-block reward at the present position on the curve. In fact, I believe there's been at least one block with less than 50BTC reward in it, and it was accepted just fine.