Adding themes; adding offline access; adding IMAP, POP, and SMTP support; allowing labels to be treated like folders; allowing forwarding; adding in-browser chat; adding keyboard shortcuts; adding online preview and viewing of many documents, including notably Microsoft Office formats; adding contact groups; adding muted conversations; adding to-do lists; integrating with calendaring (Gcal didn't even exist when he wrote that article, let alone integrate tightly); and adding synchronization with BlackBerrys. And that's off the top of my head.
Gmail's UI may be roughly the same as it was in 2005, in the same way that Outlook 2007 is basically the same as Outlook 2003, but the actual experience has markedly changed and improved--certainly enough that I think his claim could be reasonable then, but moot now.
Gmail is pretty much the same, sans themes and offline access.