Lists like this are so bogus. It penalizes companies that actually sell a product behind their main web site like Freshbooks and my own Shopify (30) but rewards sites that are the product such as tr.im.
Only in the top10 there are 2 URL shortener (ow.ly and tr.im)
I think I overestimated for a long time the concept that you really need an original idea to make money with the web.