Even though most print service providers should have no problem outputting a native Illustrator file, there are some advantages to submitting your Illustrator job as a PDF. Doing so eliminates the need to gather up images and fonts, since everything is included in the PDF. It prevents casual editing (and the resultant errors).
Since Illustrator speaks fluent PDF, creating a PDF is a Save As function, not an export operation. There is rarely a legitimate reason to go the long way around, generating PostScript and cranking up Distiller to create a PDF. Don’t feel guilty—do it the easy way.