If your sites meet Google's criteria for the Top 10, then they'll be displayed there - it's as simple as that.
Dominating a single niche can be useful, i can create many websites selling the same product. I create sales teams specialized at selling to our conversions (sales inquiries) in this niche. People tend to go to multiple sites before they finally choose one to purchase from. By having all of the sites they see you have a monopoly on that keyword phrase. This in turn leads to profits.