I've seen this mentioned a few times here in hacker news and among other blogs and forums as well. As I can see, People who want to run a US based company, but don't want to migrate to the US often do this. Where as people who want to migrate to US prefer Valley for obvious reasons.
What is the appeal Delaware has?
"Why Corporations Choose Delaware"
http://corp.delaware.gov/whycorporations_web.pdf