Well, #iranelection was the #1 most popular news topic on Twitter in 2009, according to their blog (http://blog.twitter.com/search/label/2009), so there is an actual motive available.
Regardless of the presence of motive, the execution (i.e. juvenile website defacement) doesn't exactly imply high-level cyber ops. And an easily fixed DNS hijack isn't really going to "take twitter out of commission" or whatever the purpose of this supposed cyber attack would be.
