I also used to be wed to the Adobe DNG file format because I used a separate cataloging tool (MediaPro). If one really uses LR or Aperture as their all-in-one tool as they are designed, you don't necessarily need the DNG format. The big two selling points for DNG were (a) a single file for image data, adjustments and all your metadata (no sidecar files), and (b) no worries about later lack of support for your camera native raw file format. I think for major camera makers there is little risk of file format no longer being supported once the images are in the catalog. And if you use the all-in-one tool as your catalog, no worries about the sidecar files being lost since they don't exist. All the data is stored inside the catalog database.
With Aperture you also have the choice of storing the photos "inside" the Library or only referencing them from wherever your have them stored on disk. I like having them "in" the Library because that puts everything in a single "Library" folder. If I'm using Aperture as the all-on-one tool it is designed to be, why not?
What do others do for archival format and storage?