I talk a lot about Speech on this blog because I consider it an excellent way to learn communications skills, same as being a salesperson for years or learning to act.
My philosophy has three parts; Talking, Thinking, and Testing. Talking, again, is about communication and poise (talking through your composure and staying composed). Thinking is about philosophy and planning far into the future based on ideals, and testing is about the numbers and getting out and trying things so you can see how to get better at them.
In my Charisma Major I focus on these three components, and right now I'm working on Talking/Poise. I often get asked why speech? Obviously it helps make me a more charismatic communicator, but so does selling cars really well or being a stellar actor.
It's partially personal, I've done speech, know what to expect, and it's something I'm good at. Much better at than selling cars or acting (though I am getting into Dramatic Interp this year...). But the rational (read: thinking) reason to do Speech is that speech has much more variety than sales or acting. True, you can go out and try to sell all sorts of things, but not at once. Likewise, acting requires a plethora of skills and abilities, but it also requires either contacts or a degree from an established institution. Both of those fields are limited by their established nature, in a way. You need to go through the channels to get the benefits.
I like speech because I can go out and in one weekend (If I'm ridiculously good :)) Give six impromptu speeches, six Extemporaneous speeches (Impromptu based on current events with 1/2 hour prep), six persuasive speeches, six After Dinner speeches (funny persuades), six Dramatic Interpretations and six Informative speeches. The three different types of Speech teach how to talk in the three different languages of my philosophy; Limited prep (impromptu and extemp, as well as Debate in many ways) teach how to test and use what you know, Public Address (informative, persuasive, partially after dinner) teach how to communicate learning, and Interp teaches you how to get feelings across and all the nuances of connecting with your audience.
Now, obviously I won't be doing six events at once, but I will be working on those three different areas at any given time. So in one week of working on my current speeches I'm learning all the aspects of communication if I do one event from each of the three areas. I bet you could do that in Sales or Theatre, but it requires a lot more background work before you can do it. In speech, it's almost a given.
It's pretty much the same thing that motivates me into a lot of my activities; it's the easiest way to achieve all of my goals for the moment at once that I've found. Once I start doing an interpretation event I'll be learning everything there is to know about applied communications every weekend I take my events out, or every time I go in to coach.
That's why I do speech. Shortest distance between me now and more charismatic communicator me.