Say you have a racial that increased the amount of expertise by 1% while you have a certain weapon equiped. Now lets say you only have that type of weapon in your main hand. Does the value of expertise beyond 6.5 now decrease?
For example, you have a gnome with the shortblade specialization. You have a sword mainhand and fist offhand. Your expertise value's are at 7.5%/6.5%. How much would the EP weights of expertise drop? I can't imagine it would drop tremendously since offhand attacks getting dodged would effect our energy gain, but would it be better at this point to reforge into haste instead of expertise or keep stacking expertise until you're at 8.5/7.5? I tried to math this out, but its well beyond my tiny little mind.
If you have a racial that gives you bonus expertise, but only to your mainhand (IE, mace/sword mainhand as a human, dagger offhand) you will not need to cap expertise for offhand strikes. Expertise has practically no value beyond 7.5 mainhand.