Because the MB is not as sleek as the MBP, no aluminum casing. LED backlight, illuminated keyboard. From trying both out, also MBP felt better to use.
Now with the MBA though, its given me all that plus more. Now I can just have an imac as the 24/7 home computer.
This is exactly what we've been saying. You didn't want the Macbook Pro because you needed a Pro laptop; you wanted it because you wanted a lighter Macbook with aluminum, backlit keys, and an LED screen. Well now you've got it in the MBA--but that doesn't mean the MBA's a UP MBP. It's basically a UP MB with three borrowed features from the MBP.