Blue-chip stocks are the bedrock of investors' portfolios. The household names that pay reliable tax-effective dividends have also produced good capital gains over the long term.
The big banks, Woolworths and Wesfarmers (which owns Coles) have market power that makes their profits seemingly secure.
But globalisation, advances in information technology and regulation threaten even these market behemoths.
Woolies and Coles still rule the supermarket sector, yet their dominance is not what it was since the entry of competitors such as Aldi and Costco - and could be further hit if Amazon goes into fresh food.
Part of the reason the Australian market is becoming more attractive to foreign players is our rapidly growing population.
There's a tendency for smaller countries to have higher levels of market concentration as they lack the scale to support too many competitors.
While Australia is still among the ranks of the tiddlers in terms of population, its population is one of the fastest-growing among the rich countries.
A report by the Grattan Institute debunks what most of us hold to be true - that Australia is a country whose economy is dominated by oligopolies.
In fact, the degree of dominance in Australia is no worse than other high-income countries with similar populations, the report says.
The report confirms that, indeed, where few firms dominate a market sector, they do usually earn higher profits and customers do usually pay more than they would in a more competitive market.
But it looks as if, in some sectors at least, competition is breaking out.
We are seeing that with Telstra, whose dominance of mobile is being threatened by new players. With more than one million shareholders it's the most widely held stock of all and has cut its dividends so it can invest more in the business.
Though the banking sector's oligopoly appears more secure than other sectors, there could be regulatory changes to come from the forthcoming royal commission that could threaten the market power of the big four banks.
One of the most profitable sectors is that of internet publishing, which includes the rapidly growing online platforms for employment, housing and car advertisements.
As the report says, the print and broadcast media were once highly profitable but have struggled against competition from online media.
Some the best performers of the Australian sharemarket include these types of stocks, such as real estate site REA, jobs site Seek, Carsales.com and travel booking site Webjet.
The report notes the cost of hosting additional searches or advertisements is low, and the value to advertisers and users of participating on a platform increases as more join it.
They are early movers who have been able to achieve scale. But even in internet publishing there are risks for investors where market dominance could be short lived.
Though barriers to entry to internet publishing are low, that can be a double-edged sword.
"These 'network effects' can provide strong competitive advantage, though a seemingly dominant firm can also rapidly lose its position," the report says.