While some Linux variants provide root access, others promote the use of sudo. How are they unique for each?

Many Linux commands have Unix counterparts. Why is this so?

When using Linux, there are a number of built-in procedures for assuring atomic actions on variables that may be used to prevent common race conditions. But what happens while working with single- and multiple-processor systems?

When creating Linux, why did its creators choose with a kernel that doesn't allow for preemptive multitasking? In a single-processor system, why would you want to use a non-preemptible kernel? But why does employing a system with several processors reduce the value?