I noticed the cheaper one says "no serial port" but the back of the alienware unit seems to have serial and parallel ports from looking at the photo. I could be wrong in interpreting the picture, though.

They seem to be on a similar platform, definitely Alienware and that other company are getting their parts from the same supplier. I doubt they're identical units, there's probably some differences in components (although the load-out DOES look strikingly similar).