What triggers emails on work item creation

I just tried the following:

1. As user A, I created a new WI; prior to the initial "Save", I assigned the WI to user B.
2. As user A, I created another new WI, but this time I did not assign it to a user on creation; only after the WI has been saved, I assigned it to user B and saved the WI again.

User B received Email notifications in both cases:

1. User B received a "full" summary of the WI (i.e., containing Summary, Status, Description, Type, Project Area, Owned By, Subscribed By, Id, Creation Date, Created By, Restricted Access)
2. User B received on an update information (i.e., Owned By)

Both Emails stated that user B received the respective Email due to user's relationship as "Owner" of the WI.

In summary, this looks like the answer to your question is:

1. Yes, owners are able to get an EMail notification from WI creation / assignment.
2. If they do not, the place to check is the Mail Configuration in the CCM User Profile (CCM > User Icon > View My Profile and Licenses > Mail Configuration) and check, what "owner" rules have been disabled to prevent your user from receiving the appropriate notifications. (In my case, user B had checked all options in the owner column)

Based on my reading of the terms of the users email config

they can get email when they ARE the owner, when some ELSE SUBSCRIBES them to a workitem, or when they are ASSIGNED an approval.

I do not see 'when I become the owner', only when 'I AM the owner'.

so, I think this notification (becoming owner) is not sent by design

On create, ONLY subscribers get email.

edit:  looks like I am wrong on this one. I see the entry in the mail config.. just don't have reliable experience with it.