When was the last time someone told you about an app idea and you had any vision of a Win32 (or WPF) app? The web is the defacto app platform for desktop today. Sure, there are some legacy and niche apps that are native on desktop, but mostly everything new is web based on desktop.
Mobile is a different story, but I think its due mostly to the fact that mobile HW is still changing rapidly. New sensors and other capabilities to tap into, where a standards web has to catch up. But I think this gap too will go away as mobile HW matures.