That's true with most businesses. I know from my own business, I have my top clients (20% of my clients) where more than 80% of my business \ income comes from and then rest which only just manages to make up the final 20% of my income.
For my top 20% I need to spend very little in advertising \ cost of sales to win big $$$ from them. For the other 80% I need to spend very big $$$ to win a very small number of $$$.
And to win a new customer is very big $$$. I can easily speak with 50 potential customers to come away empty handed. Furthermore to start getting a return on one customer it can easily take months.
This is the problem I have with bean counters. They are given way to much power without a true understanding of business in general.
Now for QF, I would say a good percentage of their flights contain non-status pax \ once a year pax \ BFOD pax. It has no doubt taken a lot of time and effort to convince these pax to fly with them. They have had to put up web ad's, billboards, TV ad's newspaper \ magazine ads, and sales, and even then if DJ comes along and trumps them, then it's gone to waste (excluding brand recognition).
Where as for a QFF like me, if I need to fly somewhere, I'll go to their website, give them a call, or go to my TA and book a flight with them with very little prompting. Even if they stopped all advertising (which is expensive) I'd continue to use them. Whilst there is a degree of brand loyality and a degree of "comfort" I get from using QF (eg I know what the procedures are, I know roughly what I'll get on board etc...) there is nothing stopping DJ from stepping in and convincing me to jump ship, and whilst I am loyal to QF, no one likes to feel that their loyality is being taken for granted. That's the sort of thing which will destroy a customer \ supplier relationship very quickly.
Just my 2c from someone who runs a business without having a "day job" to fall back on if I mess it up...