Very good point indeed. Monsoon system results due to complex interaction between the atmosphere, land surface and ocean systems. So it makes more sense to treat it as a coupled ocean-atmosphere-land system, rather  purely as an atmospheric circulation problem alone. Especially Indian monsoon system is understood to be a resultant fluctuation of the Continental Tropical Convergence Zone (CTCZ). The advance or retreat relate to the flcutuations (north - south movements) of the tropical circulation bands .  So we see both the aspects of circulation and movements as well. CTCZ is a atmospheric circulation (band of clouds circling the globe in west-east direction near equator)which oscillates north-south , due to land-ocean thermal contrast effects.

well, It can not be termed a circulation. Monsoon basically originates due to the north to south temperature gradients over continental India. Also, strong heating over this part makes the air to rise up and drags the westerly flow basically from Ethiopia and somalia streams towards the continental part, where westerly moist air becomes south-westerly, and rises up, finally turning into a huge synoptic system and clouds, resulting into rain over indian continent.

Yes, it is coupling between Ocean and atmospheric circulation.

I think you have to define the term "monsoon" first, which is traditionally known as "Monsoon is the term for the wind that carries heavy rains to southern Asia, and the rains themselves." and sometimes the dictionary also mentions the winds, "a wind in the Indian Ocean and southern Asia that brings heavy rains in the summer"  

So the monsoon rains in SE Asia and India seem each year to ebb and flow, but that moisture is actually traveling around the planet, only producing clouds and raining whenever it hits Pseudomonas-producing plants or is not suppressed by the atmospheric Dust Clouds, like those situated over Pakistan-Arabia or the North Africa.  family of Dust Clouds.

When the India monsoon moisture hits the Americas, it produces rains and more recently hurricanes and floods in our SW desert, the the people of the SW USA correctly call this period their "monsoon" season also.   I have attached the two Dust Clouds that inhibit  the formation of monsoon rain clouds out of the monsoon moisture each year, and also form a wall that can stall the rain in one place, causing floods like in northern India recently. 

When you overlay the Dust Cloud and the monsoon rainfall in India for example, you see a much clearer picture of how huge the effect is on the rainfall cause by the Dust Cloud on a daily basis.