Server parts are a higher grade quality parts. And the motherboards have special server chipsets. Probably 60%+ of the dedicated servers you rent today are just regular desktop motherboards (regular desktop computers on server duty). Unless you get a high end server.
Think about this the most your going to want to run your server is one to two years tops. By then your website(s) should hopefully outgrow your your server and you will be in need of a upgrade. No only that you have to think about the reliability factor. Do you really want your websites that are making you $$$$ on a old tired server? Any decent website(s) is going to give the server a pounding. You start running into PSU and hard drive problems, they are usually the first to go. You can save yourself anywhere from $200+ by just using desktop parts.
You could seriously build yourself a $280 server and it will run your websites just fine. Or you could build the same server with server grade parts and spend $600 on the same server. And they both are going to preform the same job. I spent $1,000 on my server if I would have used server grade parts I would be looking at $1400+ for the same server. And I plan on replacing the server next year. So I saved myself $400+.
