You're from Slovakia right? Is there any article about the subject? Do Slovakians have an opinion of this?
It is true that players have more leeway regarding the team they play for at the World Cup. The reason is it is not an IIHF event. All tourneys governed by the IIHF fall under the IIHF rules, the World Cup, for example, did not in 2004.
Dainius Zubrus played for Russia on the 2004 World Cup team, but retains his ability to represent Lithuania in IIHF events.
On the broader topic, there are older threads that we could probably track down on the topic of international events and changing teams with all the details about the prior rulings and changes regarding IIHF rules, as there have been modifications and appeals over time.
note: my comment was regarding the World Cup comment not Slovakian's perspective on the Stastny's. Included wrong post in the quote, sorry about that.