If they call it "iWeb" and name it among the other apps, I'd say we can safely assume it's a standalone app that integrates with the other iLife apps. So its center is the "web". Yes, I'd say this is about templates (I personally hate them, but iLife seems to do everything with templates) that let you easily create webpages. Since it's from Apple, I'd assume it actually makes _good_ webpages, too. (They _do_ have "standards compliant" people in the Safari team...)
Let's hope it's not too restricted in what it lets you do. For example, I'd hate it if you could only really use it in combination with a .Mac account. We'll see early next week.