Using an intent to edit calendar event doesn't work

So I don't think you're doing anything wrong - I put together a basic implementation of the same thing via command line and the same restriction applies:

am start -a android.intent.action.EDIT --es title "New Title" content://com.android.calendar/events/1

I'm only able to edit the same fields you are - You might be better off doing a ACTION_VIEW and letting the user decide to edit (sorry I don't have a better answer for you, that's kind of annoying)

Workaround for this problem: If you use Intent.ACTION_VIEW you'll at least get an activity in which you can hit the Edit button, after which you can edit the title and location and everything else (in the default calendar app anyway).