Ostensibly, the allocation of spots is based, at least in part, on performances at past World Cups. The best way to compare the weak confederations (Africa, Asia, North/Central America) is to measure the group stage performances of the qualified teams, since so few advance to the later rounds.
I ran the data for World Cups back to 1994, and here are the results:
|Points per team in group stage|
**** This mark is based entirely on Australia's 2006 performance.
The standard arguments given against further participation from CONCACAF is that the region has only one strong team, Mexico (more recently, two). I dispute the merit of the argument, but even if we accept that argument, removing Mexico's results from the picture yields a CONCACAF number of 2.13. If we do the same for the best African side over that period, Nigeria, and the best Asian country, Korea, those confederations put up 2.29 and 2 respectively.
Population as an argument doesn't hold water: the most populous Asian countries (China, India, Indonesia) have done nothing at all at World Cups, and as federations go, CONCACAF is only marginally smaller than Europe.
Do I think CONCACAF deserves 4 full spots? Of course I do. Asia doesn't deserve what they're getting, and I'll be shocked if they don't prove to be the worst performing confederation at South Africa.
Who's with me?