While it's true that all eTapestry databases come with this standard Report Category, since this category name can be changed or modified at any time, chances are that someone from your organization re-named this standard report category at some point in time (which would explain why you can no longer find a category named: "System")...

If you are unable to locate a report category by the name of "System" in your organization's database, please note that this is NOT cause for concern... Any resource that specifically references selecting the "System" category when building a new report/export is merely using this as an example of a report category that you may store a new report or export under. If you don't see a "System" category in your database, simply select another report category or you could even add a new Report Category and name it "System" (so that your org does have this category available going forward).