Digital players REA Group and carsales.com cash in Young couple using a laptop. REA Group realestate.com and carsales.com showed the spectacular - no, the fabulous - growth dynamics of the digital advertising world in all their simple, stark glory. They are the mouth-watering combination of high double-digit revenue growth and even faster top-line profit growth. So that their already high margins - thanks to the low-cost base compared with non-digital players - move even higher. Although, as I noted a year ago, while they are all still fabulous, the carsales numbers show clear signs that the business is now starting to stabilise or mature. Still, to stress, around a high-growth, high-margin dynamic. Not yet so, with REA, a subsidiary of NewsCorp, owner of this paper, which remains on that stronger digital growth path. For the year REA revenue was up 21 per cent and EBITDA (earnings before interest, tax and depreciation) was up 30 per cent. As a consequence the EBITDA margin was up from 45 to 49 per cent. That is to say, nearly 50c in every revenue dollar came through as profit. And most of that, apart from the tax paid, ends up falling to the shareholder bottom line, as these digital businesses tend to run with cash surpluses and very little 'D' and 'A'. Now carsales is a little further along the digital growth curve. Revenue growth has slowed progressively from 30 per cent, to 27 per cent, to 21 per cent to now 17 per cent in the past year. Although, it's worth noting, that precisely because of that previous fabulous growth, 17 per cent last year generated more actual dollars than 30 per cent did three years ago. Back then, though, the 30 per cent sales growth generated a 48 per cent leap in gross profit. In the past two years, profit growth has more or less kept pace with revenue growth. This meant that after carsales lifted its gross profit margin to around an almost unimaginable 55c in the revenue dollar, it has managed to hold it there - indeed, it actually clicked up to 56c in the latest year - on still strong, if no longer outrageous, revenue growth. In the latest year that was still 17 per cent. Compare that with the 4-6 per cent or so of the most successful of the old-style pre-digital businesses such as Woolworths and Coles. And trust me, Coles and Woolies do not make 50c in the sale dollar.