Interesting NY Times story on the rationale behind President Obama's first Oval Office speech. In sum, a speech from behind the presidential desk conveys a sense of national importance and universal application -- this is not a speech meant for a specific group of people in a specific geographic location, but instead is directed toward all of us.
Using the nature of presidential communications as symbolism is an artifact of the twentieth century's technological revolution. Presidents in eras past might well have chosen a specific venue with an eye toward symbolism, or chosen to address a specific group of people. President Lincoln's powerful Gettysburg Address is a paramount example. Radio and television have made it possible, however, for the president to convey messages instantaneously, and the manner in which they do so helps to frame the way citizens receive their words.
President Franklin Roosevelt was the earliest master of this technique. His "fireside chats" were meant to convey a sense of security, of familiarity and even friendship, of intimate involvement on the part of the federal government and the president personally in this national (and even international) crisis -- and overall, they worked.
A few decades later, President Kennedy's speech at the Berlin Wall, while remembered for his self-identification with a popular local pastry, was a powerful symbol of Western resolve (even as historians have found that in reality, the administration was not altogether displeased with Wall's construction).
Symbol and sentiment, words and meanings. The ways in which we communicate with each other are rich and multifaceted. We would do well to carefully consider the ways in which we interpret and understand each other.