Apple working on 10", 13", 15" tablets [rumor mill]

From a Gizmodo source "that has always been 100% reliable" comes the rumor that Apple may be working on a 10, 13 and 15-inch tablets, with "one running Mac OS X."

Hmm.

Apparently the "two touchscreen prototypes—made of aluminum, but on the shape of big iPhones—were in a factory in Shenzuen, China," one running Mac OS X 10.5, the source claims. It's unclear whether the units were for demonstration purposes, preproduction or just units made to throw the hounds off the trail.

It's been widely reported that Apple has experimented with several different sizes of tablet to appeal to CEO Steve Jobs' perfectionist tendencies.

I take this rumor with a grain of salt, as should you. Why? Because to deploy a new device that's so far untested in the market is ballsy enough -- deploying three sizes of that device indicates a confidence that the device will be a guaranteed hit.

That's a problem, for a few reasons:

1.) The tablet form factor, up until now, has been a niche market;

2.) It takes a lot more expensive tooling and production to manage different sizes of a device, and Apple tends to minimize its production versions for efficiency (one Snow Leopard OS version; three MacBook Pros, one MacBook, one iPhone form factor retooled for iPod touches).

3.) It's unlikely that a company would launch a new device with several iterations (example: iPhone);

4.) Many people get by with a 13-inch laptop. What are you going to do with a 15-inch tablet without a physical keyboard?

5.) The multiple-OS thing doesn't make sense. One or the other or a modified version.

But that's just what I think. What about you?