This is pure speculation on my behalf, but here's my take:

• The closest competitors to the 630 are the 420 and the 730.
• A lot people are now backing out from the 630 to shop either of the other equipment due to the many problems that have overshadowed the 630.
• Most people will not go with a 730 as it is too big and expensive, so they will be spending less money on a Dell system than what they originally planed.
• By making the 420 more expensive, Dell is gaining on that bit of non-spent money, since most original shoppers for the 630 already have that budget set apart for a new computer, so they spend it in the 420.  The deal turns even sweeter for Dell as probably they are making even more money than they would selling the 630 cause the new profit margin on the 420 is probably higher.

Of course, I could be completely mistaken! :)

Rafa.

You will find that prices change very quickly at Dell and offers come and go routinely. The important thing to do is design a system you will be happy with and that you can afford.

Well you have to look around for a deal on the xps420 mine just cost me this week,

the price was $2600 I had a 25% coupon which brought it down to $1950 I got the Q9400 processor

425 watt power suppy, nvida 9800gt, 4 gb memory,keyboard and mouse bluetooth ,media card

reader internal,sound blaster x-fi extreme gamer,a dvd rom and a dvd +/-rwdL,Dell a525 30 watt2. 1 stero speakers with sub woofer,Mcafee 3 year security 9.0 , A 3 year warrany on the computer Plus adobe Premier Elements photoshop elements and sound booth software.Oh yes a 750gb serial ata hard drive.plus a 24 iinch ultra monitor model number 2408 wide digital flat panel.I also got the floppy.

 Simple answer - GREED and word to the wise....

RUN do NOT buy a Dell especially the XPS420.  I have wasted more time and money trying to get this piece of junk to work and after them replacing the motherboard, sending a replacement printer, and now wanting to replace the motherboard AGAIN and the printer AGAIN -- I am trying to get them to take the thing back but hmmmmmmmmm now they don't return calls as promised which of course I'm sure is intentional on Dells part so I am now further outside the return period. 

I have never experienced such HORRIBLE customer service - it is a complete joke