I've been a Mac user for 6 years now, and have loved every machine I've purchased. Having said that, I'm a certain kind of user who matches the machines that Apple sells. I want mid- to mid-high range hardware, capable of pretty extensive multitasking (which, in my experience, works better under OS X than Windows), and the ability to do graphics design and layout (I admit, this was much more hardware-constrained in 2003 than it is now). Macs are a pretty good fit for the featureset that I want, and are price-competitive with Windows boxes.
HOWEVER in the ad, Lauren wants a machine with a certain amount of raw horsepower, a keyboard she likes (which, with Apple, is either entirely true or entirely not) and a 17" screen. That could mean a wide variety of machines -- processor architectures, memory, integrated or discreet graphics -- but Apple, when you want a 17" laptop, assumes you're a higher-end user, that wants a very well engineered battery, a lot of horsepower, a fast dual-core CPU, etc. etc.
Lauren doesn't. She doesn't want a lot of those things. She just wants a computer with a 17" screen. Apple doesn't sell the machine she wants -- but because there's at least 3 or 4 PC brands at any Best Buy, she can walk in and get what she wants for a fraction of what Apple sells it for.
It's a question of mapping: the goal isn't to take an APPLE to start with then compare it to the price of a similar PC; instead, it's to take a PC you want, and asking if there EVEN IS a similar Mac -- in a lot of cases, there just won't be.