ccTLDs do not have to follow ICANN rules. They are treated as sovereign territory of the country they belong to. On a ccTLD the registry can take your domain from you at any moment for any reason.
That's not the case. The ICANN is an entity independent from the US. Well, that's not entirely true, but true enough that the US can't just take a .com from someone just like that.
Frankly, I would prefer if the USA just used .us (and .com.us, .org.us, .gov.us, etc) as a ccTDL and left .com, .net, .org, etc to be under the supervision of the UN.
Don't see much of a difference there.