No it doesn't. A customer wants a Mac, that is the target market. Like all successful companies Apple has created a product line. Look inside a Mini, iMac or MBP and what do you see? The same thing! Same chips, same capabilities, just minor differences and a different board layout. They just take the same ideas and repackage them. A different purpose and target market would be between the iPhone and the Mac. Within the Mac line they're essentially the same, with variations to fit whatever specific the customer wants. The MBP can certainly act as either a desktop or mobile regardless.
You're comparing a Xeon with dual GPU's against a monitor with a consumer CPU inside which is the largest difference between the Macs. Any way you cut it given the BOM on the new Mac Pro the chances of it coming in at $1.5k is practically zero IMO.
A laptop and a desktop are not the same market. That is like saying a car and a mini van are the same market. Also, you are assuming that all Mac Pro's are going to come with a dual GPU. We shall wait and see though.