That's an extremely selective quotation from the nutshell text. The essay (which I originally wrote, so I'm pretty familiar with it) gives three basic check points to verify whether it's likely that an xkcd reference is helpful: this reference meets none of them. It is at best a trivial and non-free illustration of an SQL injection attack, which has its own article anyway. People are prone to arguing that a given xkcd strip provides some unique insight into a subject when this is usually extremely subjective. Were this actually the case for a given reference then one would imagine that some third party would pick up on this in a reliable source. That hasn't happened here, so it seems like nothing more than one Wikipedia editor's personal judgement. WP:EL specifically notes when external links are appropriate and again this link doesn't meet those guidelines as applied to the rest of the encyclopedia. Chris Cunningham (not at work) - talk