Pretty much every startup success story has an "and then we got spectacularly lucky" part to it. In Viaweb's case, it's more like "and then, for the nth time, we almost died, then somehow didn't", but the idea is the same. It's one of the great unmentionables in the startup world, and understandably so: succeed and you want the credit; fail and any mention of luck sounds like sour grapes.
I've heard a lot of startup founders talk about a lot of startups, and only Marc Andreessen (of Netscape fame) both realized and admitted to the large role luck nearly always plays.
I should add that great startup success stories almost always involve founders who were awesome as well. (Netscape and Viaweb both qualify on this count.) It's just that being awesome isn't enough. Traf-O-Data had awesome founders, but it failed; those same founders, Bill Gates and Paul Allen, had better luck in their second venture.
I've heard a lot of startup founders talk about a lot of startups, and only Marc Andreessen (of Netscape fame) both realized and admitted to the large role luck nearly always plays.