The US hasn't asked for their extradition for conspiracy either, and yet they have for Assange. Unless being accused of raping women in Sweden causes the US to do that, there must also be some other difference between Assange and those other journalists.

We don't really know what threats have been delivered to them, only Assange is high-profile enough for whatever happens to him to send message. For all we know those other journalists received a friendly phone call and capitulated immediately - or more likely, they're simply not as big a target.

I mean, some of the other journalists include Wikileaks members and Assange supporters who've personally assisted Snowden in escaping to Russia. If it's an intimidation strategy, it's clearly not working.