Two apps from Microsoft Office suite, OneNote and Lync are available as Windows 8 apps with Metro UI on Windows Store. But Word, Excel, PowerPoint, Outlook aren't actually Windows 8 apps. The core of the new suite runs on Windows 8's desktop environment. Office 2013 is available on Windows Store but just with a link to the desktop version.
Why didn't Microsoft go all the way and build Office 2013 as a Windows 8 app?
In an interview with Mashable, P.J. Hough, Microsoft's vice president of Office program management said the company does have plans to offer a modern (Metro) version of Office suite. "We're committed to delivering a full set of Office experiences on Windows 8," says Hough. "We've gotten a lot of experience from OneNote and Lync, and we're going to continue down that path.