The US is a much larger country than countries like Germany or France. If you add up a roughly equal-sized amount of the European Union for comparison, you get a number of hosts around 30k-ish, which is somewhat lower than the US's 34-35k, but not by all that much.
The BRIC (Brazil Russia India China) are still considered developing nations. In that context the level of industrialization is probably lower even though they are much more populous.
As for China it's not impossible that they are already monitoring for that and blocking Shodan from accessing their Internet.
