Now, the degree to which peripheral computer functions are located on the motherboard or off has been the primary variable in the development, and in many ways motherboards have moved to both having more and less peripheral functions actually located on it.
The more modular the device, the more useful it is to have peripheral functions located off the motherboard, even though the system is still quite centralized. This particularly applies to laptops and other highly customizable pieces of hardware. Such motherboards typically have lots of sockets that other peripherals may be plugged into.
Devices that aren't modular, however, such as televisions or cell phones, tend to have all their peripheral functions located on a single motherboard, termed an integrated motherboard. This is by far the cheaper and more space efficient of the two motherboard models, but simply isn't practical for many devices.
So, peripherals tend to be mostly located on the motherboard, or mostly off, with little in between. Over time, these two opposite trends have been increasing.