Strategies for Arguing

Obama's quote about our destiny being like the 50 stars is an analogy used to invoke emotion and tie together many related issues in one all-encompassing sentence.  He means that we are supposed to work together to achieve our destiny.  This is an effective way to carry his message to his intended audience because as Americans, we are very prideful in our country, so the 50 stars part really carries that well.  Also,  as Dillard suggest, words can be used as tools to explore a topic and "dig a path", which is exactly what Obama's quote does.
Classification is when you group items according to their similarities.  An example would be grouping houses by the style of architecture they are built in.  Using classification is a good way to organize and explore a topic, as is comparing and contrasting.  To compare and contrast in your writing, there are two ways to do it: block and point by point.  When using block, you compare and contrast each topic separately, one after the other.  When using point by point, you combine the topics into one and compare and contrast from there.  Either way can make your writing more effective to the reader.  Williams uses different method to make his writing so effective.  Instead of just listing off events without description, he includes dominant impression and visually takes us through the events, making it seem like we know what it was like.
From the start, Steve Jobs experience with cancer effects pathos greatly. Just talking about it effects it I think.  But as he went on in his story it got more and more effective.  First, when he talked about getting ready to die, and secondly, when he talked about the details of the surgery he underwent.  The entire thing effected me pathologically.  He obviously wants to effect his audience in that way.  As I read through, I was so wrapped up in the sadness of the story that it shocked me in the end to see what the point of the story was.  I think he hopes to effect people that way to make a stronger point in the end.
On another note, humor is a great way to convey a point in writing, as long as it fits the context of the audience it is being delivered to.  In the passage from the Onion, a more serious message about the lack of focus on academics at Florida University is made.  It is humorous, while conveying a clear point which makes it appropriate to use in the passage.
And lastly, reiteration emphasizes and supports an argument very well.  That is one reason why Martin Luther King Jr.'s 'I Have a Dream' speech has resonated with Americans for so long.  Repetition makes writing more memorable and in a lot of ways, powerful.