I can't STAND licenses that don't define their terms properly - in the RPG industry there are some clip art collections with that kind of license ("this excludes use by "mainstream" publishers). At least this one gives a list without a "such as" clause.

From how I read it this license breaks down as follows:

- Mainstream comic publisher - license fee
- Indy comic publisher - no license fee
- Any other published works for profit - license fee
- Any other published works not for profit - no license fee