That's the literal truth: There is no separate Start menu within Metro itself, and even when you're in Windows 8's more traditional desktop mode, pushing the Windows key doesn't bring up a Start menu like you're used to. Instead, it kicks you back into Metro. In addition, the only place you'll find power options such as Shutdown and Restart is inside Metro. For all intents and purposes, Metro is what the Start menu has morphed into in Windows 8.
And what a Start menu it is. In earlier versions of Windows, the Start menu was little more than a set of shortcuts to documents, folders, and programs. For Windows 8, Microsoft has enhanced it with live tiles that can display real-time data and even run full-blown apps. Microsoft could have called the new features the Active Start Menu or Start Menu Extreme; instead, it's known as Metro.
That's all you really need to know -- again, that is, if we're speaking in the context of the traditional Windows desktop experience. When you include new and emerging user experiences, however -- such as tablets, smartphones, and devices such as TVs and consoles -- Metro takes on a larger and more significant role. I'll get more into that in a minute.
Developing for Metro mode
What does Metro mean for developers? That's easy: It means you can write apps that run on Windows, in the same sense that you can write them for smartphones.
Microsoft has caused some confusion by referring to apps for its new Start menu (really, the Start screen) as "Metro-style apps" -- as if there was some other style for Windows. It even seems to have begun referring to traditional Windows software as "desktop apps." This is a poor choice of words, because there isn't much comparison between the kind of desktop Windows software you're used to and the apps that run in Metro.
You'll never see a Metro-style face-lift of Photoshop, Word, or Excel. These and similar applications will continue to run in the traditional Windows desktop environment (which in the Windows 8 Developer Preview looks virtually identical to Windows 7). Metro's touch-optimized UI simply isn't suited to these types of complex, feature-rich, professional applications.
Furthermore, Metro apps don't even really coexist with desktop applications. Metro apps always occupy the full screen -- they can't be arranged on your desktop alongside other windows. You can usually copy and paste between the two styles of software, but that's about it. If you right-click a document in Windows Explorer and choose Open With, you won't see any Metro apps listed among your choices.
Instead, think of Metro as a mode -- one that engages when you press the Windows key -- and think of the apps you create for it as programs designed to run in Metro mode. Metro apps are designed to be simple, fast, and easily accessible. They're like smartphone apps -- and this is the important part.