I'm quite sure in future releases and/or updates that MS Will add more personalization options for the Start Screen. We see hint of this in Blue.
Let's look at it from a business standpoint of finances and time. I'm quite sure they allotted an X amount of money and time to write the code of 8 and release the initial product. They can always add to it just as they've done with past OSs.
Keep in mind that this industry moves exponentially quicker nowadays. Releases of new products and concepts change rather quickly. e.g. How often do the new iPhones and iPads with hardware and software get released? Can we say what we buy today is already obsolete? They are already working on the "next model". I think that's true with most products. Yes?