I would agree that top to bottom Europe is the strongest region on the face of the earth, but that is why it has the most WC slots by far. 53 teams vying for 13 slots in UEFA versus 35 teams trying for 3 1/2 berths for CONCACAF (the 1/2 is competed versus South America - in 2010 Costa Rica lost out to Uruguay)
1-out-of-4 teams make it in Europe, less than 1-in-10 make it in CONCACAF, so in terms of difficulty, it is obviously a much harder road to make it out of CONCACAF.
The quality of UEFA teams 14-20 versus teams 4-10 that don't make it in CONCACAF, overall the European teams would beat them on neutral fields, but kay20 has pointed out that trips to these mostly Central American countries are downright hostile. You guys could argue 'urine bombs' versus laser pointers, but there is no way you can compare Ireland playing in say Bosnia or Slovenia versus them playing in El Salvador or Honduras, it's much more of a home field advantage for the CONCACAF teams, a lot more hostile for the opposition.