Graham's claim is correct. This bug affects all *nix systems (ie. unix, linux...). Since more then 50% of web servers use apache (which runs on *nix), and about 14% use nginx (which runs on *nix). It's very easy to see how this is as big as Heartbleed...
I'm sure someone will argue "you shouldn't be using bash for CGI anyway"; but one way or another most common web scripting languages (e.g. perl) do make use of system calls which then potentially touch bash.