I totally agree with your comment about WORDLE serving to highlight the commanlities.
As an EFL teacher, I tend to focus a lot on the common words in English, as these are the words that define our fluency in the language. I use the BNL2709 vocabulary profiler for this at http://lextutor.ca/vp/bnl -- when you compare McCain and Obama's use of the most common words in their speeches, it can be a good starting point for a compare/contrast analysis which is accessible to most EFL students (well, those above B1 on the CEFR scale).
When I get a good result for a WORDLE, I save it to the public gallery. Perhaps interesting to view WORDLEs focusing on the common words in English below with your WORDLE of unfiltered words in the McCain speech in mind. Compare the two WORLDEs
http://www.wordle.net/show/wrdl/289555/Obama_Speech_5-11-08_-_BNL2709http://www.wordle.net/show/wrdl/289552/McCain_Speech_5-11-08_-_BNL2709
Notice the differences in frequency of words in both speeches (campaign, bless, nation, unite, promise, achieve, white). Also of note are the words that appear in one and not the other like fail, victory, generation. :)
Creating complementary WORDLEs like this can be another useful way to explore the compare/contrast issue that you mention.
Idea posted to a blog about using Wordle for getting the gist of a weather forecast. The author has taken the words from a weather forecast and asks the students why they think certain words are larger than others.
"Doesn't each writer hope that people find their blog interesting and helpful? I believe the answer is yes. Besides writing an interesting article, it helps to make the blog posting accessible through the reader's use of search engines and access to related articles as they read your blog posting."