Can you explain the reasons?

After some quick googling, I found more references to this claim, but only in comments on articles:

http://www.networkworld.com/community/node/37608: "The use of a corporate jet is often required by corporate policy intended to protect the executive from the threat of violence or abduction. "

http://www.swamppolitics.com/news/politics/blog/2008/11/auto...: "Most corporate CEOs in companies with corporate jets are REQUIRED to use those jets as their ONLY mode of travel, as per the insurance requirements of being the Chief Executive Office and Chairman of a Publicly Traded Company.".

> "Most corporate CEOs in companies with corporate jets are REQUIRED to use those jets as their ONLY mode of travel ..."

That would make getting a cup of coffee from the local café a serious PITA. I guess that's why they have executive assistants?

Don't forget the restrictions on who-can-travel-with-whom. This tends to complicate things a little more.