[tdrgabi]

Yes. We could argue that people would still buy tickets even if they weren't available online, since flying beats car / ship traveling even if you have to walk to a store to buy your ticket.

[mseebach]

That's not the point.

Selling and advertising tickets online is at least as good as the offline alternative at the same cost (presumably cheaper). Otherwise, why bother?

Thus, better/cheaper online advertising -> more tickets sold -> higher demand for air planes.