Although I agree with what Krieghund said, the double standard for the US navy is mostly for game play IMO. In reality defense of Iceland was turned over to US forces in July of 1941 (5+ months before Pearl Harbor). USAF began land based air patrols in the N Atlantic, and US war ships started escorting Atlantic convoys from Newfoundland to Iceland shortly after.
For game play on the Euro side US ships must end their movement adjacent to US territories (exception sz102). This is done so once the US goes to war it takes the US 2 turns to get to Europe so they can't be ready to pounce the turn they go to war (other then landings in Brazil, Iceland, Gib, or N Africa). If the US was allowed to station itself off Iceland (while neutral) they would be able to make an impact one turn sooner by merging w/UK fleet off England, threatening Norway, or even the French coast (w/naval base build).
On the Pac side (as Krieghund pointed out) the US has many possession (islands) throughout the Pacific. If they were confined only to sea zones adjacent to the US territories it would still allow the US considerably more freedom of movement in the Pac (much more so then in Europe where they are basically stuck in port).
The Japanese navy is a much bigger threat to the US on the Pac side then the Germans are in the Atlantic though (just the way it is in the game), plus the Japanese can move through, or share most sz's with US ships while the US is neutral. IMO the US is allowed to roam more freely in the Pac probably so they can attempt to block out the Japanese from making direct attacks (exception being a J1 attack), or make adjustments if the Japanese move into their waters while US is neutral. It also allows the US to move up into a better position (Queensland NB) if the Japanese head south towards India.
Using Krieghund assumption of protecting US interests in the Pac, plus the fact that while neutral the US isn't allowed to end naval movement in sz's adjacent to Japanese possessions (guess the Japanese would see this as an act of war?), I think the game would be pretty interesting if two things were adopted (even as a house rule).
1) The US had similar movement restrictions in the Pac as they do in the Atlantic where ships must end movement next to US territories. One exception (like in Atlantic sz102) allow US war ships to do patrols into sz9 (allows the US to block Japan from coastal US while US is neutral).
2) Japanese surface ships can't enter/pass through sz w/US surface warships, or end movement in sz's next to US territories w/o a DOW (similar to US ships can't end movement in Japanese waters above) because the US would see that as a threat, (I would allow Japanese subs to be in, or pass through US waters/ships while the US is neutral).
Just think if there was no J1 attack, the way the US islands are positioned (Midway, Wake and Johnson) to the west & south of Hawaii the US could effectively use a dd screen (if they had 1 more) to block out the Japanese surface fleet from a direct attack on Hawaii launched from the Sea of Japan, or the Caroline Isles naval bases. The Japanese would have to basically use only subs and air power to hit Pearl (more realistic), or move the Japanese fleet to sz 14 to threaten Hawaii/San Fran. It would also keep Queensland from being used as a launching pad into the DEI for the US fleet (the US fleet wasn't stationed off Australia until after the Japanese attack).
Just food for thought WB