While I really don't know how much it costs to manufacture these things, we can still do some analysis.
Cost difference estimation done with the help of Newegg.
Graphics
Another discrepancy - Gateway says this laptop has no dedicated graphics, but you claim it has a 128MB dedicated graphics card. The MBP has a 256MB dedicated nVidia card. If your laptop does have a dedicated card, I'd still put that at $50 MBP advantage. If it doesn't, that's a whopping $300 or so in the MBP's favor.
Chassis and Weight
Plastic (?) 5.84 lbs on the Gateway, Aluminum 5.5 lbs on the MBP. Sturdier design and 0.34 lbs lighter, let's put the price on that around $30.
Optical Drive
Blu-Ray/DVD on the Gateway, Superdrive in the MBP. $50 in favor of the Gateway for the Blu-Ray.
So, yes, a MBP is expensive. They're probably making a good profit. A 30% profit margin puts the MBP around $1700, which, if you look at everything I've laid out, is about right.
First an all aluminum body versus plastic, is at least a $200 upgrade, probably more. The complete layout is far better, the trackpad is better, the keyboard is better, the build quality is better (machining is far more precise), and the body is more rigid.
Then a Blu Ray upgrade from a DVD burner is more likely $100.
Finally, the video card in the $1700 MBP is the 256MB 9400M, and the video card in the $2000 MBP is the 256 MB 9600GT/9400M.
But the 9600GT or the equivalent in the next generation MacBook Pro is not really a $300 upgrade even if thats what Apple charges for it. More than likely its somewhere between $100-$200.
Also you forgot the screen is much better in the MacBook Pro, thats probably a $100-$200 difference or more!
This isn't really the point I was making, but regardless, to address your post...
The gateway doesn't have an i3, it indeed has an i5 processor. It was simply mislabeled. Read the thread I linked to in the OP if you don't believe me.
Regardless, your math seems off, and you seem to have overvalued apple's parts.
For example, you claim that the 2 year old GPU in the Macbook Pro costs $300 more than than the just released 128 mb dedicated ram GPU in the Gateway, which seems like quite a stretch. There's no way the 9600 costs more than $60 nowadays.
In addition, you post says that you can get a Macbook Pro with the dedicated graphics card, a 500 GB HDD etc for $1700 when in fact, a Macbook with those specifications costs $2300.
Again, the video card in the $1700 MBP is the 256MB 9400M, and the video card in the $2000 MBP is the 256 MB 9600GT/9400M.
Then its really irrelevant what the 9600GT costs, the point is the next generation MacBook Pro that comes with a dedicated video card, the video card will be a $100-$200 upgrade on Windows machines, even if $300 on a MacBook Pro.
Where as Intel graphics come along with the processor and are the bare minimum for current GPUs.