They should; however, the keyboard shortcuts for Services menu commands are only requested by the supplying application. macOS assigns these shortcuts and has ultimate control over which application or service gets what. If the DEVONthink Services menu items do not have shortcuts assigned, it is likely that macOS assigned these shortcuts to another command, or that they are used by the current active application.

The operating system relies on information supplied by the current application to determine which services should be shown in the Services menu. For some applications, often those developed for both Mac and Windows, this information may not be what's anticipated. When this occurs, certain services may not be present. For example, selecting text on a web page in Firefox will display the service DEVONthink: Take Plain Note. The same text on the same page in Safari will show that option as well as DEVONthink: Take Rich Note.