"In a desktop app is I can add 100% of the web. But the web can only add like 10% of the desktop."
This is so true. On the Mac, Cocoa-Webkit integration is so great that nowadays almost every desktop app contains at least some "web" components, such as Webkit-backed UI, basic web browser, or HTML-backed rich text controls. On Windows, .NET is also moving towards web-friendly integration. Although the latter is not yet on par with Cocoa-Webkit integration (it's harder to manipulate the internal guts of DOM and Javascript with .NET—AFAIK), it's making progress.
The other direction, i.e. making web app more desktop-grade, is harder. My colleague zonble has deadpanned with this question: "How would one drag-and-drop an image to your gmail?"1
Use this desktop app, which is yet another example of integrating web into desktop app is the easier direction. ↩