I'm working on setting up an image gallery for a client using the built-in gallery feature.
I'm not sure why, but some of the linked attachment pages look more like regular post pages, while others are fairly sparse (I've not set up any template files for attachments at this point). Since they are all image files and were all added through the gallery creation system for that page, I'm not sure why they were treated differently.
Here's the gallery:
And two attachment pages (note the different linking structure):