In my experience things scale linearly in the homebrew range fairly well. Certainly, malts and sugars do. I have taken 5 gallon (even 3 gallon) recipes up to 15 gallons and done everything linearly. For my palate I couldn't taste any dramatic differences with the hops.

However on larger scales of 3bbl systems to 10+bbl systems its more of an issue it seems. And I think it is at that scale that we get such information about scaling concerns.