It actually is pretty standard. Sweden has done it in many other cases. As Wikileaks highlighted when this was made into an issue.

IANAL but it seems that Sweden has agreements with certain countries to enable questioning of someone who's not in the country. When it comes to EU states it's pretty straight forward.

One thing that would complicate this matter is that there doesn't seem to be an agreement between Ecuador and Sweden regarding this. Given that JA was under Ecuadorian jurisdiction it's entirely possible that this was one of the reasons why the prosecutor didn't go down that route initially.

Sources (sorry, can only find them in Swedish):

http://www.regeringen.se/sveriges-regering/justitiedeparteme...

http://www.regeringen.se/sveriges-regering/justitiedeparteme...

It's pretty standard to go to the police for questioning when they can't/won't come to you. In the US you can assert your 5th amendment rights not to answer questions, but as far as I know Assange hasn't said he won't answer questions.

For America Yes, for Europe no