"However, if I can expand this to Top Cow or Avatar I'm helping the sales, however small, on my Marvel books because I'm almost certain to pick up some new readers"

In this quote, Mark Millar is talking about the potential advantages of expanding his work to other comics publishers such as Top Cow or Avatar. He believes that by doing so, he can not just increase sales for his Marvel books, but likewise bring in brand-new readers. This is since readers who might not have been familiar with his work before may be drawn to his composing through his cooperations with other publishers. By broadening his reach and getting new readers, Millar hopes to not just benefit his own sales, however likewise contribute to the success of the comic book market as a whole.