Shopify offers a fully hosted SaaS solution. Shopify Plus is built to handle any level of volume allowing high-volume merchants to focus on their business—not their IT.
Shopify Plus is built on the same infrastructure that supports over 350,000 Shopify merchants, ensuring that flash sales, Black Friday, or heavy daily volumes can be handled without any speed or reliability issues.
During flash sales, existing Shopify Plus merchants are processing peaks of thousands of checkouts concurrently. Offloading concerns around scalability and performance allows you to focus time on energy on value-added pursuits such as brand building, storytelling, marketing, and customer-experience.
Both Magento Enterprise and Community have many examples of clients that operate at super high scale. In fact, Magento 2.0 is designed with scalability in mind—but this scalability comes at a cost. On-premise deployments require that you architect your servers and infrastructure to accommodate the anticipated single highest peak in traffic. This means building out and managing an infrastructure that you may actually only use for a single day each year. Any time you roll out a change to production, you risk impacting the scalability of the overall architecture.