Incorrect. You can easily maintain a 'bastardized' version of DCS with both Steam modules and Store modules running side-by-side. It takes about 15 minutes of prepwork, and from there, Steam -will- handle updating store modules. Updates that are shipped to DCS through Steam contain the necessary files for updating all aircraft, regardless of ownership. EDIT: To clarify, Steam doesn't 'update' each aircraft, but updates the game and all aircraft together, so it will cover store modules.
If you wish to try and maintain a version as I've described- one where store and steam modules are side-by-side, PM me and I can assist and provide support. I even wrote a tutorial on how to set it up, it just gets drowned out by those whom don't know any better.