It works well for popular flights within Europe, but if you want to fly to bit less mainstream destination given your starting point (even something like Katowice -> Las Vegas, and back), you may end up on transfers between different airlines, or the return part of the journey may be via a different airline. Booking through Expedia, Kayak etc. is basically the only way (I know) to handle this with zero hassle.

The expedia example was from the article not from me. Airlines could set up phone lines for direct purchases before the internet.