The problem with Google is that they don't seem interested in doing the hard work to go from 90% of the way there to a full product. It's like that with nearly everything they do. Often, it shows up as a US-only policy (flight search currently fits that bill). Other times, it's just random things. There are no Apps accounts for Google+. There's no "Tablet Optimized" section of the Android Market outside the US (and of course no books or movies either, but that's not their fault necessarily).

Most people aren't going to be interested in replacing something that works with something that sometimes works. Google might have a great flight search engine, but if I have to use Orbitz 30% of the time, I'll just use Orbitz. I already have an account set up there, and I can actually buy the ticket instead of having to find the flight, go to the airline web site, and search the flight again to buy it.