[lukatmyshu]

Orbitz/Expedia are travel-agents --- kayak/ITA Software are simply aggregators of flight results. There is a world of difference. For one thing, I am not sure how Kayak would be able to handle an itinerary that has multiple airlines in involved (take AA from SFO->Bangkok, then continue on Bangkok Airlines to somewhere else for instance).

Additionally, with a travel agent (like Orbitz/Expedia) you buy your ticket through them, and you can contact them if your travel plans change. I recently (last week) was unable to board my flight to Thailand because my passport expired in <6 months. Even though my ticket was not refundable, the terms that orbitz had with my airline allowed me to cancel (after I missed my flight) for 200 dollars. That experience alone has made me rethink booking any airline faires directly through the airline website.