I decommissioned a document management system at my client, a smallish law firm, because the system was too complicated, insecure, and expensive. Updating it to run w/ the latest version of MS-Office would have cost thousand$ just for the s/w. We replaced it with Google Search, and we defined a file hierarchy and naming convention for all documents created after the switchover. Client is very happy, their file access is more efficient, and they saved a bundle of money on administration, not to mention all the h/w and s/w they never bought.
Obviously documents are the lifeblood of any law firm. These guys only have about 100,000 or so, less than the aerospace company in question, but the lesson applies. It's extremely unlikely the IT admin of the aerospace company has the resources to manage, much less install, a proprietary document management system.
The ONLY reason to have a formal document management system with a database (like Microsoft SQL *ugh*) is to control access. But access control is something that really, really should be done through the directory. So unless you're NASA or another organization with many, many millions of documents and a legally mandated auditing requirement, there's no reason to make this more complicated than necessary. And even then....
Of course, if we're talking about images with no searchable text, that's another story.