I think they designed it with a wooden deck, rather than concrete. I'd be afraid to add concrete because of the weight (the pool area is up in a section of the yard held by a retaining wall).
Would you agree with Moderator Steve about using 2X6's rather than 5/4 ? I'm going to be selling the house in a few years anyway, I think, and the pool will only get used a few months a year, and not too heavily even then. Do you think 5/4 would hold up for at least 4 seasons or more?