Re: why Airbus advertises?
7gcbc pretty much answers the question, but there may also be a measure of "Co-operative marketing" going on.
The airlines may well want their customers to be happy flying on their Airbuses, so it could be part of a deal that Airbus does some core advertising on brand awareness as part of a package with the airlines, and the advertsing spend counts as part of the sales package.
Same goes for foodstuff advertising, you don't go to a Danone shop to buy chilled yoghurts etc, you go to your local supermarket. But Danone see the marketing spend as something that is worth money to the supermarket chains and thus count it as part of the cost of sale.