Not necessarily, once you've got a number one position there's...

Not necessarily, once you've got a number one position there's less advertising and promotion required - think of it this way: when carsales was new there needed to be advertising answering the questions 'what is it, why is it better, why should I use it?' Whereas now it can get away with 'nudge' or 'reminder' style advertising because we all know it

Now think of how long the tv spots for the first type of advertising had to be versus the second type - the second would be shorter, therefore less spend. Obviously it's an oversimplification of only one kind of ads but it's a useful exercise to visualise how ad spend can drop off for number one players without eroding the advantage.