gluLookAt

Okay I was reading the Camera5(strafing) tutorial on www.gametutorials.com And found out that I suddenly became unsure on some vector stuff, namely the center param in gluLookAt() When he is calculating the way to move forward he does this:

	// Get the current view vector (the direction we are looking)
	CVector3 vVector = m_vView - m_vPosition;

Where m_vPosition gets passed as eye param and m_vView as center param in gluLookAt() Now comes the part that my mind wont get, why does he have to calculate the View vector? Aint the m_vView vector the view vector? And if it's not then why are he does this ? I know my math skill in vector math is poor, so plz explain it in as plain words as possible. Entire function:

///////////////////////////////// MOVE CAMERA \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\*
/////
/////	This will move the camera forward or backward depending on the speed
/////
///////////////////////////////// MOVE CAMERA \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\*

void CCamera::MoveCamera(float speed)
{
	// Get the current view vector (the direction we are looking)
	CVector3 vVector = m_vView - m_vPosition;


/////// * /////////// * /////////// * NEW * /////// * /////////// * /////////// *

	// I snuck this change in here!  We now normalize our view vector when
	// moving throughout the world.  This is a MUST that needs to be done.
	// That way you don't move faster than you strafe, since the strafe vector
	// is normalized too.
	vVector = Normalize(vVector);
	
/////// * /////////// * /////////// * NEW * /////// * /////////// * /////////// *


	m_vPosition.x += vVector.x * speed;		// Add our acceleration to our position's X
	m_vPosition.z += vVector.z * speed;		// Add our acceleration to our position's Z
	m_vView.x += vVector.x * speed;			// Add our acceleration to our view's X
	m_vView.z += vVector.z * speed;			// Add our acceleration to our view's Z
}