2eNose
Почему "Процесс - это и есть тот самый "первичный" поток."? Конечно, в обыденной речи так можно называть, но всё-таки это разные понятия.
Вот в MSDN написано:

About Processes and Threads

Each process provides the resources needed to execute a program. A process has a virtual address space, executable code, data, object handles, environment variables, a base priority, and minimum and maximum working set sizes. Each process is started with a single thread, often called the primary thread, but can create additional threads from any of its threads.

All threads of a process share its virtual address space and system resources. In addition, each thread maintains exception handlers, a scheduling priority, and a set of structures the system will use to save the thread context until it is scheduled. The thread context includes the thread's set of machine registers, the kernel stack, a thread environment block, and a user stack in the address space of the thread's process.