Uhhh not really sure what you mean by your question but I’m guessing you meant why don’t you get higher megapixel images with the SLR lens hook up for the iPhone? If that is what you mean, then the answer is because that’s not how it works. The size of the image isn’t determined by the lens. The lens would only determine the focal depth and aperture of the images taken.

Thanks @uberbatman. I was wondering whether this setup would yield better photos than the ordinary lens on the phone. Also is the 8 megapixel limited by software on the phone?

The resolution is determined by the CCD (Charge-Coupled Device; the part that turns light into a digital signal) in the camera, not by the lens. All the lens does is affect how the light hits the CCD.

The DSLR has electrical coupling to the lens to control functions like auto focus and f stop. I can’t tell from the write up if those connections are there. If not you will have to do it manually. The iPhone has some authority built in so if you are close it most likely is good enough.
Also the DSLR can put high resolution pictures in cache so you can do a high speed burst of 5 or 10 or ? frames. I am not sure the iPhone can do that.

DSLR will dominate phone camera’s because of aperture and speed shutter control amongst other details.

You asked: “if you hook up an SLR lens like this you still only get 8 megapixels on the iPhone right?”

You are correct. You can’t add pixels by attaching a lens to any camera. Pixels represent digital representation of what is captured.

That’s really expensive.. You will get better pics with this:
http://www.amazon.com/Canon-PowerShot-Digital-Stabilized-Wide-Angle/dp/B0075SUK14/ref=sr_1_5?ie=UTF8&qid=1355770595&sr=8-5&keywords=camera+%3C%24250
only $215

Speaking as someone who has the camera @RocketGuy posted I can say its a great camera for a relatively low price.

@uberbatman Does that camera run on AA batteries? Can you tell where it was made?

@LuckyGuy No and thank god, I have another camera from canon that does and my god that thing eats batteries like no other (like when I take it out I need to bring 8+ batteries) As to where it’s made, no clue.

Sorry but that sounds AND looks just silly. Wan’t to make good photographs? Get a real DSLR camera and bunch of lenses.