I was working similar idea, but for laws. They also change quite a lot and not very well presented online.
I halted the development after I realized how complicated can word diffs get. I would be interested about techniques that you used. I it is quite good as it is, but I noticed some common problems, such as:
1. Reusing letters from words that have nothing in common:
> fury over a [-hik-]{+n increas+}e in bus fares [1]
2. Inserting few paragraphs into one word (first paragraph) [2]
3. Loads of minor changes, also more of 1. [3]
[1] http://newsdiffs.org/diff/263401/263432/www.nytimes.com/2013...
[2] http://newsdiffs.org/diff/265812/265841/www.washingtonpost.c...
[3] http://newsdiffs.org/diff/265776/265810/www.nytimes.com/2013...