Why do the DEVONthink Services menu commands show no shortcuts?
They should, however, the keyboard shortcuts for Services menu commands are only requested by the supplying application; Mac OS X itself assigns them, and therefore has ultimate control over which application or service gets what. If the DEVONthink Services menu items do not have shortcuts assigned, it is very likely that Mac OS X gave them to another Services command or that they are used by the application that is currently frontmost.