Discussion on: You can write whole website in just single web page.

Yes, but this is

• Terrible for SEO [More pages is better, each one with custom urls]
• Terrible for performance, If you have a 10 page site with images, you'd be loading all of it at once.

Still a neat trick though :)
The "target" bit might be useful in other situations, for example for "tab" navigation within content.