The price difference is actually more than I thought.... See this:
That may not be as equivalent as you think. To match the low end MBP here are the choices you have to pick.
I started with the base XPS 1530 with 2GB.
-Processor to 2.4GHz
-LED 1440x900 screen
-250GB 5400 disk (I know the low end MBP has 200, but Dell didn't offer that. It was 160 or 250, so I went for "at least as good".)
-Video to 256MB
-Dell wireless N
-Dell Bluetooth 2.0
-Integrated Soundblaster Audigy (This may be debatable, but Apple includes optical 5.1 capable output and optical input. I'm not sure Dell's built-in audio can do surround, so I went for the sound upgrade here. The X-Fi may actually be more equivalent too, but I went for the middle pick as a compromise. I don't know if either allows for optical in/out.)
I left software out of the choices, but remember Apple includes iLife 08.
Total price was $1863 (US) for the Dell. That's just $150 off the base MBP, and the extras from iLife would likely make up the difference if you bought equivalent Windows software. Dell also doesn't do multi-touch trackpads.
So, the cost of "close as possible" to a MBP shows that Apple isn't really charging too much. Now, if you don't NEED any of that extra stuff, then you can save money by not paying for it. But if you're going to get that stuff, too, then you should not ignore Apple simply because of cost.