Maybe there are no Steelbooks planned for R3?
I believe the Philippine market is too small for local distributors to order 'Steelbook' casings, so either other R3 countries have Steelbook casing (makisalo lang tayo) or they have to be creative as Magnavision does with Incredible Hulk and American Gangster. But with this one, instead of tossing out the R2 discs and replacing them with R3 ones, Magnavision decided to just let it stand as it is... Especially since there are no (?) complaints with the one disc PAL version. Just my speculation..
Whether selling different region disc is allowed, I think movie distributors has decided against enforcing it, otherwise how could Amazon sell R1 discs to us? All local distributors break that rule sometimes (Viva with R1 High School Musical, C interactive with R1 LOTR, and now Magnavision with Wanted R2). Whatever, I am not complaining, the more the merrier...
Finally, Why? Because Steelbook sells, many people will not buy regular DVD (but wait for it to go on sale) but would snap up Steelbook because most often they don't reach the sale bin... And people who buy Steelbooks are often the higher-end who are more likely to be knowledgeable about HT, and thus have unlocked players...
Just my thoughts...