As far as I know, and I could be wrong that every photo in the iphoto library is jpg
This is untrue.
In the iPhoto Library every file is stored exactly as imported - Raws as raw, Jpeg as Jpeg, tiff as tiff etc.
iPhoto is about Photos not files. So, whether a file is a jpeg or Raw is of little consequence to it. It treats them all the same.
When you process an image the decisions you make are stored in the iPhoto database and your original file is not touched in any way. When you view the shot, the decisions you made are applied to the image live, and can be changed at any time - this is why it's lossless editing. This applies equally to Raw and Jpeg, lossless and lossy formats alike.
In common with all such lossless editors, the only way to access your processed image is to export it to a new file - and this can be in Jpeg, Tiff or png. (You can, of course, export the Original - but that's not processed)
To avoid the tedium of always having to export anytime you want to email a quick snap to your grandmother, iPhoto generates previews. These are "good enough for most things" versions of the edited shot, and they are what's used in the Media Browsers and what you get if you drag from iPhoto to the Deskop. These are Jpegs.
But if you want better quality versions of your photos then you can use the File -> Export route.
As iPhoto is about Photos, it's not especially interested in the File Extension. It's more concerned with the Kind of the shot. So, in the info window it will tell you if it's a Raw or a Jpeg or a Png.
Regards
TD