No, they didn't get wealthy merely by building something that people wanted - if you just do that, other companies will offer the same thing and the market will drive down the price to just above the cost of production. This is how the free market is meant to work and it's what makes it (in theory) an efficient way of allocating resources. In order to get truly wealthy you need to find some barrier to entry, some way of ensuring that you can avoid the free market and its drive for efficiency. It could be network effects, which ensure that competitors to sites like Facebook and eBay won't succeed because they're useless unless everyone's already using them. It could be software lock-in and patents of the kind that drove Apple to be one of the richest companies in the world. It could be information asymmetry that causes people to choose your well-known brand over cheaper but better products because it's too expensive for them to assess the actual quality of what they're buying. But there has to be some barrier, some way of defeating the free market.