Apple isn't using smaller and smaller drives for the MacBook Air. The current release goes up to 512GB which is the max so far. And 10 years worth of high res photos and movies is always going to take up space. Why doesn't he just buy an external hard drive like a normal person or use Dropbox/S3 etc ?
And Apple apps don't go to great lengths to hide photos. They are stored in your Pictures folder in a package e.g. Aperture Library. Just right click and your photos are there. Packages are great for inexperienced users since it is easier to backup and less opportunities to mess up the metadata.
And the metadata is stored inside the iPhoto/Aperture library package. For Aperture at least it is an open standard XML file so there is no 'lock in' what so ever.
And even Finder quicklook seem to render the full .jpegs just fine and fast enough, so wasting so much disk space on a useless preview/thumbnail feature (to me) is a dealbreaker. I'd even be willing to accept missing or postage stamped thumbnails, rather than having to uninstall applications and remove music to make room for my photos.
Aperture and iPhoto use same library DB packages now, and Aperture's a cheap upgrade if you've outgrown iPhoto's consumer family interface. Aperture lets your organize any way you want, to any depth, with nesting of any kind within any kind.
Split across different folders depending on whether you have edited them or not.
Other enthusiast friends of mine hate the package approach because they're very used to the file management approach, so YMMV.
And adding a separate drive is cumbersome, and slow, and not a solution for a tablet at all. Plus iPhoto doesn't easily support libraries on a external drives. I think you need to launch it while holding Option or something arcane like that.
It's like attaching an anchor to a 13" Macbook or Air.