Nevertheless, if 1) it were the case that users always need to open documents in an external application, and if 2) it were the case that there are no special advantages to opening documents in their own windows inside DEVONthink, and if 3) it were the case that DEVONthink prevents the user from opening a document in an external editor, I would agree with you. If those premises were true, the default of double-clicking a document in a view window should be to open it in the default external application.
I don’t agree with those premises, and think that the argument that double-clicking on a document to open it under a default application is like arguing that Apple should have reserved ‘Command-I’ either to open the Info panel of a file selected in the Finder, or to apply italic formatting to selected text in a rich text document - or to further extend the argument, that the user should have a Preferences option to choose the environment in which ‘Command-I’ is functional.
DEVONthink provides several views of database contents. In the Icon and List views, and when a group is selected in the Columns or Split views, a view of document contents is not provided. The natural command to open a selected document, double-click, is used. The document is opened in its own window. That command is also applied in other views, even when a view of document contents is available.
There are advantages to opening a document in its own window. That window can persist as long as the user wishes to work with a document, and it is in the rich environment of DEVONthink, which provides tools and assistants that would not be available in an external application. For example, I often open a document in its own window and can open a set of related documents using tabs, so that I can explore See Also, See Related Text and Option-click on a word to explore a set of related items, regardless of their filetype, and relate notes to documents in tabs.
True, there are times when it’s desirable to open a document in an external application, not only for editing, but for formatting and other features that cannot be duplicated in DEVONthink, which cannot attempt to render all documents as they were originally created, or provide all editing functions of a filetype. For example, MS Word’s display in DEVONthink provides access to the body text content of the document—and so contains its primary text information—but cannot render the actual formatting and layout of the document as it can be rendered externally. But when external access is desired, there are at least three ways to do that.