Netscape was certainly what Joel Spolsky was referring to in terms of never rewriting software (http://www.joelonsoftware.com/articles/fog0000000069.html). They dominated the browser wars in the early days since they released their browser much earlier than IE, with the added cost of technical debt. I'm not sure what ultimately caused their downfall, but I suspect it wasn't due to their codebase, but rather an inability to figure out how to properly monetize their large userbase.