How would you get to 90 that way?
As much as I would like to assume the bonuses would apply to both hands, if that were the case, I see no reason to have an off-hand skill at all. If your culture provides +15 and your profession gives you +25%, which would follow the same arguement, you basically just end up with the same starting skill in both hands. That's clearly not RAI.
Now, some interpret Javelin or Dagger as both melee and thrown, in which case the argument for sword bonuses applying to both hands kind of makes sense...but again, it defeats the purpose of ever mentioning an off-hand rule.
Edit: Nevermind...I see this has already been clarified.