Technically no (outside of the video shared memory requirement), because of what was said an element of that RAM is used by the OS for its housekeeping which further reduces the RAM available to programs.
Why "about" 4GB? Why isn't it an exact number? That's because the PC uses its total memory space not just for RAM but also for such housekeeping chores as remembering your hardware and maintaining internal scratchpads and "stacks."Any memory addresses remaining unused after the housekeeping requirements are met will be available for use as general-purpose memory. This represents the amount of RAM you can actually use.
It’s not unusual for a PC to need almost a full gigabyte of addresses for internal use, so putting 4GB of RAM into a standard 32-bit system usually nets around 3.2GB of usable RAM. The rest of the 4GB of RAM is there, but the system has no way of accessing the memory because your PC has run out of internal addresses.
So starting with 4GB rather than starting with 3GB would leave you more after the housekeeping and shared video requirements are taken into account.