I am not about to add Apple's online store into the mix. No sense in comparing apples to oranges. I will say this however:
Apple hardware costs more. It is made by Apple, or it is made in collaboration with Apple. I am glad it is only made by Apple. The quality is higher, the price is higher, and not as many people buy it. I like being a user of the minority Operating System. Ask any *nix user how they feel about being a minority user. I am sure at some point they will have something positive to say about not having to deal with viruses and spyware. Mac OS and *nix might not be more secure by design, but it is more secure based on usage.
Back to the Apple's online store: Apple knows simplicity. Their online store is just nice to use. It is not cluttered with a gazillian options that you do not care about. I would vote Dell's online store to be the most overwhelming of all. It is a nightmare.
Based solely on my opinion, I like the Alienware store a lot more then the Dell store. It is easier to choose your options on the Alienware site, and Alienware does not try to shove software and other hardware down your yapper like Dell does.
* At the time of this writing, Dell has 10% off their Desktop systems.
Dell Dimension XPS vs. Alienware Area 51: These are Intel Pentium 4 based systems. They could both be called gaming systems, they could both be called graphics systems. I call them workstations. They are used for web design, multimedia, 3D modeling, gaming, etc, etc. In other words I do not see the Alienware as more of a gaming rig.
Some might say these systems are configured with too much horsepower, and it is not worth the price. It is true you could cut down on anything and save money. I however do not like to compromise. And I have seen the bad things that comes from compromising on computers and I do not like it. In general I want to be able to throw more then I usually would at my computer and see if it will crush under pressure. I like to see it perform above my expectations because I know that if I stay with a system for a while those performance benchmarks will be decreasing exponentially every year. My computer before my 500 Mhz PowerBook G4 in 2001 was a PowerMac 6400/200 circa 1996. If I am happy with a computer (unlike my Alienware rig) I will use it for a while.
Here are the specs of the Area 51 and Dimension XPS in no true order. It is interesting to see how one or the other store has the same options plus or minus $10 here and $5 there. I am not comparing the specific prices. I left out all the extra crap that both online stores tries to push on you.
3 year Tech Support P4 3.2GHz 800 Mhz FSB
Windows XP Pro
1 GB DDR RAM
128MB DDR ATI RADEON™ 9800 Pro
250 GB Hard Drive
CD-RW & DVD-RW
Sound Blaster Audigy 2
Dell: $2,346 (theoretical price w/o 10% discount is $2580)
These differences in price are negligible in my book. It always depends on what month or day or hour or minute when you buy from any of these online stores because you never know what type of special deal you might get.