Is there any reason why this site is limited to London startups? Does this geographical restriction add any value over a national startup map?

Hint for Londoners: Zoom the map out at bit and it shows other places. These places have names like Bristol, Manchester, Glasgow, and are located in the areas of the UK that are not London. People live in these places, and there are startups there too.

In fact, there's already a good UK startup map: http://techbritain.com/