You think they are higher? I know hundreds of people who can solve the rubik's cube and less than 5 percent of them are abel to do it in less than 30 seconds. I teach a class on how to solve the rubik's cube as well and of the 45 or so students each semester who come into my advanced class only 2 have ever been able to solve it in less than 30 seconds starting off. Very few people actually take the time to do this event seriously. Of those who do, I would say at least half of them go to at least 1 competition and if there are only 17, 000 people on the WCA database, then there are roughly 34,000 "speedcubers" in the world. Lets say, to be generous there are 40,000 speedcubers in the world, if the WCA database is any indication of what percentage of speedcubers are sub 30 then somewhere around half of that 40,000 speedcubers are sub 30, so 20,000 max and I think the actual numbers are more like 40%. I haven't taken the time to do this research thoroughly, but I don't think my numbers are that far off. In fact I think they are a little over.
I would be interested to see the real percentages if anyone wanted to do a study of the WCA database.