I agree and I also noticed the same last week end.
Sending email is probably last task in most work flows so I would do it using using Java mail. If considerable number of emails need to be sent with some transaction, I would use MDBs. For inventory, WS in most cases is good option.
May be Cade wanted to keep the uniform design and any data access whether it is from DB or external systems - he end up creating DAO.
Though i also agree that both Mailing Service and Inventory Management Service should have been handled bit differently.
In my case for emailing-I have used Apache James Mail Server http://james.apache.org/ which can persist the messages and handle hard & soft bounces, takes care of SPAM, virus protection also.