Tad Williams isn't usually listed with cyberpunk authors, even though the Otherland books take place in cyberspace, with characters who are hackers, gamers, evil corporate executives, etc.
I suspect that Williams' work in fantasy for his first trilogy may have classified him as a fantasy writer, and the fantasy elements in Otherland seem to confirm that. (Characters encounter giants, Alice in Wonderland characters, etc. in the VR environment.) Also there isn't a classic cyberpunk hero. Instead of Hiro Protagonist or Neo, we have a South African Woman and her bushman student as the questors seeking out the mysterious corporate entities who are capturing young gamers in cyberspace traps.
Neither of these seem reasons to exclude the Otherworld books from my cyberpunk list. Besides, I really like them! (And Williams sure looks more like a c-punk author that Sterling does!)