Of course it's relevant. There is no lock-in preventing you from visiting other Websites which are just a url or hyperlink away. When was Google Search ruled a website monopoly? What were the parameters? Who's defined the boundaries of what a search service can do and what relevant content they can provide? At what point should Google have known they've had to cede control of their own website and invest resources in giving their competitors more prominence?

What other websites need to be wary of the same ruling and at what point do they need to focus their efforts on giving their competitors virtual real-estate on their website at the expense of growing their company?

If you have more than 50% market share in a given market you're considered a monopoly. Although practically, these type of actions aren't usually taken until around 75% market share.