as you discovered the send to menu (and also the user tool menu) can let you do a lot of stuff using your existing programs and context menu.
the advantages of the built in screenshot captor emailing facilities are:
1) you can send multiple screenshots at once (you may be able to do this via context menu, not sure)
2) you can add a list of common email recipients and select from menu in one action. [i think this is main advantage]
3) you can prefill a standard subject and message contents