To clarify there is no such thing as 'Star' charging extra miles for US to Asia via Europe. Each frrequent flyer program within Star Alliance follows its own rules for routing and number of miles required for a given award.

Under its old award chart, United charged an extra 20k miles for US to Asia via Europe. That was because Europe to Asia was 20k miles higher than US to Europe, and you were crossing Europe along the way. I havent't looked at the mileage comparison under the new (post-Dec 31) chart but assume it works in a similar way.

Air Canada recently changed its rules to allow crossing the Atlantic or the Pacific (or one in each direction) on a US to Asia award. They also now allow two stopovers instead of just one. So really valuable change there! And unlike United they don't block partner award availability ('starnet blocking'). Furthermore, their awards are now less expensive than United's, eg 120k miles in Aeroplan vs. 145k in United for first class US-Asia. (Aeroplan has been known for high fuel surcharges in the past but those only apply to bookings on Air Canada metal, and their change fees through the end of this month are only CAD$55 and will still be less than UA's except for 1Ks who are except come February).