Most of the top 1000 e-commerce sites are built on Salesforce, but most of the rest are built on Shopify and it's a very long tail. Salesforce acquired Demandware which was strong at very custom requirements. As time goes on, the number of companies who need that level of customization is closer to 100 than 1000, so customers number 100-1000 is really what this is about.

Disclosure: worked at Shopify