Is Snow Leopard really that big of a surprise?

It is rumored that Mac OS 10.6, a.k.a. Snow Leopard, will be previewed at WWDC and announced at the Macworld Expo 2009, just fifteen months after Leopard. What people don't seem to realize is that Panther came fourteen months after Jaguar, and Tiger came seventeen months after Panther. In fact, it is only Leopard that took two and a half years. For a visual representation of this, see this chart. Maybe 10.6 represents Apple's return to normalcy in its release schedule.