Both considiring there market & department
Home users find assembled better cos they have a lot of choices to select from, Intel or AMD, nvidia or ATI, etc, branded, there is usually limited choices
The worst thing with branded, fast & top of the line CPU, but 128MB RAM, 7 low end gfx card, i mean today I was looking in a paper & there was an ad of PCS computers, they were giving Athlon64 PC in Rs 25k, specs are Athlon64 3000+ with 128 MB RAM & GeForce 5200 card with 128 MB RAM, now U with only a few choices to be made when it comes to selecting other parts
The biggest reason for costly branded PCs is Licensed Softwares, which are original be it WIndwos XP or NAV or Nero, which we save money by going for assembled, since software means a CD only which can be copied we can pirate it
However, for offices assembled are a compleate no no. reason, with assembled they need to use their own assets & pay for it for the support required, like minor software quirks etc, with branded they get the service free, also when they make their yearly tax return & accounts they cannot show that they used pirated softwares as it is illegal & they can be called in the court, so they have to use original softwares, which U either need to buy seperatoly or buy with the PC in form of branded PC