FogBugz was released in Nov 2000. How big was Joel Spolsky then? (It's before my time.) It looks like Joel was hardly blogging when FogBugz was released ( http://joelonsoftware.com/backIssues.html )
To be fair, as early as 2004 he had this to say on the name:
"Yeah, it's not an ideal name... But the brand equity is already worth significantly more than the cost of having a yucky name... (There was a period for about 6 months when "Z" was all the rage. Antz, Dogz, and Atomz come to mind)."