Ok, so after looking over the descriptions of the Legendary and Limited Editions of Halo 3 on ebgames.com I noticed it makes no mention of the Legendary Edition coming with an art book but the Limited Edition does but that just doesn't seem to work. If I'm paying $130 for the Legendary Edition I think I should be getting everything the Limited Edition along with the 2nd bonus disc and helmet game case.

One of the bungie weekly updates had a break down of each unit and what it comes with.
www.bungie.net

You'll also get the Legendary Edition disc, including remastered, high-res versions of the Halo and Halo 2 cinematics; an expanded digital "Bestiarum" guide to the creatures and cultures of Halo 3; The Cortana Chronicles; and exclusive machinima episodes.

So you get a digital document rather than printed document. But it's expanded edition! ;-)