The reason AISC probably contacted you is because they sell the database for $60.00 in a number of formats. It is well worth the price and it is much more reliable that trying to create your own by transposing the Steel Manual to Excel manually which are prone to typos (not to mention the hours of time necessary to reproduce the tables). None the less, I don't see how you can be prevented from recreating the tables in the book under a copyright arguement unless you are selling the spreadsheet table. Of course, I'm not a lawyer.
My 2 cents
Gerard Madden, P.E.
Middlebrook + Louie, Structural Engineers
71 Stevenson Street, Suite 2100
San Francisco, CA 94105