Did you just pick 20 players at random to compare? I highly doubt those are the top 20 servers. Ferrer? nadal? Almagro?
Read the OP "top 20 servers of 2012, in terms of percent of service games won." Raonic is #1 with 93% of service games won and Haas is #20 with 83% of service games won.
The point of subtracting % of service games won from % of return games won is to see how much the actual serve helps the player win the game. Players like Ferrer, Nadal and Almagro actually hold serve 86%, 88%, and 86%, respectively. This is due to their ground game because they also break at percentages of 34%, 38% and 24%, respectively. Unlike Raonic's pathetic 16%.