PG mostly talks about intrinsic reward in this article. We should work on stuff that is interesting to us, and brings us fulfillment. However, I believe that Paul is missing a huge component here, and that is extrinsic reward.
Extrinsic reward complements intrinsic reward. Extrinsic reward allows us to push through the hard, difficult work that we might not be interested in, because we know the work will be rewarded. It is the light at the end of the tunnel for difficult work. PG, and Bill Gates were able to work so hard because they had internal belief that there was an extrinsic reward for all the work they were doing.
In a perfect world, we would all be completely self motivated to work on every task, but this just isn't realistic. Especially in today's working work. People like PG, and Bill Gates are able to fully credit intrinsic reward, but fail to mention that the extrinsic reward ($$) validated the hard, gritty work they put in.