Why laptop is necessary for Star diagnpsis C3/SDconnect C4?

Recently, many owners have been looking on MBSTARTOOL for Star diagnostic units but most of them really don't know why the laptop is necessary but see most come with a hard drive. Does the software need to be on it's own hard drive or can it be put on their existing drive if they have room? Here, we customer service would like to help will-be buyers out.
Quoted from users on specialized forums:
-mb--Need to connect directly into a RS232 port without using an interface - this is why I went for the complete system with laptop.

-mb--The software Xentry/ DAS is a bit slow on an old IBM so that it is worth paying a bit extra and getting a Dell D630.

-mb--There is a very specific set of COM ports you must use for it to work. For example you need DAS to be looking at COMx within the VM session, then VMware needs to redirect that to COMx which is a 'physical' serial port on your machine.

-mb--It's probably because it has a real com port. Most laptops these days have just a USB port and things don't always work right if you're using a USB to RS-232 converter. You wouldn't want to brick a component during an update if you're using USB. The other option would be to get a C4 system, but then they cost more. I think there are a couple other systems out there like IBM that also have real com ports.

-mb--The PART D mux(C3) is a serial ported mux-mb--that's the reason for the Dell and IBM older laptops.
  The PART W mux(SD connect C4) is and Ethernet/wifi connected system and that is the reason for use on other laptops-mb--the issue is the operating system currently DAS Xentry only runs on XP.

-mb--Plug and play!! It is more convenient for users because the software for C3/SD C4 diagnostic tool will be pre-installed before delivery.
According to the customer feedback, Dell D630 is the most popular for STAR C3 or SD CONNECT COMPACT C4.