Of course RSS, or other syndication, is not always a solution in every case, but I believe it is the best solution in many cases (whether you feel it was a "pat" answer of not). 
We are primarily a web hosting service provider, not a bulk email service provider, and, while we are pleased that what mailing services we offer are useful to a large majority of our customers, we understand that our services will not meet everyone's needs for email.
We provide no command line hooks at all for our account control panel driven services, and this one is no different. You *can* script using cURL to provide some of this if you have the expertise, and the patience to deal with account control panel changes that could break your code without notice, but that's about the best you can manage as we do not publish an API for our account control panel. Some of this has been done, and has been discussed (with working "proof of concept" code) in these forums.
Frankly, I think that is a painful way to approach this, because things in our account control panel change pretty often.
I can't answer your "why" questions; there are a lot of different ways of implementing anything - our web panel developers have various considerations to take into account when deciding how to implement something. In the case of Announcement lists, one of the over-riding concerns is to not compromise our Announce List's compliance with our anti-spam and mailing policies, so this is an important consideration.
Suggestions are about all any of us can do when it comes to these things (myself included), but my sense of it is that it is unlikely that you will see changes that will make it easier to send greater quantities of email, with less control of an authorized account control panel user, from our servers. That's just my feel for the situation, and not an "official" statement; but I've been around here for a long time, and I feel pretty confident that I am reading the lay of the land correctly on this. 
--rlparker
--DreamHost Tech Support