Why Was Gmail the Breakthrough for Dynamic Web Pages?

Guillermo Rauch says Gmail was the most important breakthrough in the history of dynamic HTML. Google showed that someone could download Microsoft Outlook to check mail, or open gmail.com and run the whole application there.

Apple designed Safari, in his telling, like a digital book. The back gesture feels like dragging a page. Most people credit Gmail's magic to infinite storage. For him, Gmail was the siren call: Ajax, and the realization that desktop software-like experiences could live inside the browser, so anybody with a browser could use the software. Overnight, the CD-ROM was done. Software would no longer ship physically.

Unlimited storage from the cloud meant a mail interface in the browser could reach a server without worries about backups or storage. The webpage coming alive with JavaScript is what got him into the world.