Two Laptops...
Two Desktops.
Thats how it's always been (in the beginning) and always will be.
And that sub-notebook idea... might want to think again.
Think Different
Err, what beginning are you talking about? Apple didn't start making laptops until what, the early nineties? The Macintosh Portable (ONE laptop) was the beginning, but it was kind of a flop. The PowerBook 100, 140, and 170 (is that one laptop or three?) were the first in Apple's "modern" portable strategy.
If you're talking about desktop and portable LINES, you may be right: consumer and professional lines of desktop and laptop form factors. Unfortunately, we're seeing a contraction of options within these lines. If the rumor holds true, the next revision of the iMac will move the baseline to 20" -- that may be too large to be practical for some users. The Power Mac towers used to sell for as low as $1499, but the Pro raises the minimum by a grand. The MacBook (13") replaces the iBook line that in recent years had two sizes (12" and 14"), and the MacBook Pro (15" and 17") dropped the PowerBook's smallest size (12").
Is this a good thing? I guess it depends on whether Apple feels it's better to simplify the product line at the expense of customers who want more options. It may help them in terms of retail placement, but at what cost in terms of retail sales? Right now it probably means that some of the Apple faithful will choose to get by on what hardware they have now, when they might have made the jump to new hardware had there been a compelling option. (The Mac mini threads are full of people who were waiting for the mini to at least make it to C2D.)
Don't count Apple out of testing an expansion to the product line (iPod, iPhone anyone?). Just because one foray proves unsuccessful doesn't mean Apple won't try another. (Would we have seen a mini after the failure of the Cube if Apple weren't willing to try again?)