They should just kill the format. Everything should just be drag to install, drag to trash to remove.
The DMGs are a clever way to (A) make sure the app gets to the proper location while simultaneously (B) teaching the user about what's actually happening on their computer. As I said in a sibling comment, this all made much more sense when users also launched apps from the Applications folder directly.
Some applications offer to move themselves to the /Applications folder when started the first time outside /Applications or ~/Applications. Though in general, it would be better if Apple made it more attractive to publish in the App Store, since it brings other advantages (e.g. mandatory sandboxing).
Also, personally, I sometimes purposefully put apps in places other than /Applications—for example, I like to keep games in their own Games folder. And then the dialogs are kind of annoying.