I think there are couple of things you've slightly misunderstood. I'll try and clarify.
Events
These are notifications that Inventor broadcasts out to programs that have set up an event handler. I hadn't thought about it before but based on your questions, they can be broken down into two categories; system and command events. System events are events that Inventor broadcasts out to all event handlers and are general to Inventor. These are things like a document is being opened, a document is being saved, a parameter value is changing, a command is being executed.
Command events are the events that Inventor fires that are related to a custom command that you've created. In this case you'll always be the one single handler of these events. You set these up through the InteractionEvents object which supports getting user input through selections, keyboard, and the mouse. The thing to clarify here is that this has nothing to do with standard Inventor commands. For example, you can't get events that happen within Inventor's Extrude command. All you can do with Inventor's commands is listen to the system event to be notified when a command is started.
Commands
Commands are how a user interacts with Inventor. When a command is executed it takes over the user interface, gathers input from the user, and performs some action. As mentioned above, you can't really interact with Inventor commands other than watch to see when they're executed or using the ControlDefinition.Execute method you can start any command, just the same as the user clicking a button to start a command.
Event Watcher
The Event Watcher utility is a program that lets you easily pick certain system events to watch for. It doesn't support watching any command related events, either Inventor command or custom commands that you might create.
There is another utility that's supposed to create a custom command and let you watch the events associated with that command, so it's kind of like Event Watcher for a custom command. However, I just tried it and it's not working correctly and needs to be fixed. You can still take a look at it and maybe it will be of some help. It's located in "C:\Users\Public\Documents\Autodesk\Inventor 2015\SDK\DeveloperTools\Samples\VB.NET\Standalone Applications\Inventor\UserInteraction"
InteractionEvents
The InteractionEvents object is an object in the Inventor API that supports the functionality needed to create a custom command. It supports the ability to get input from the user through events and provides the expected command behavior, i.e. when it's started the current command is terminated and the new command takes over the user interface.