Uh, let's say you are a noble, you own some villages with like 1000 (add zeroes to your taste) serfs. They rent your land to feed themselves, they pay you for it with, say, half of their production. Can it be called a commerical farming? It's not like you found these villages, it's not like you do it purely for commerical profit (likely you care more for food provisions for your levies, horses for knights and other military needs and wine to make the archbishop more agreeable, and something to pay to your liege - speaking in general terms, of course). The gentry aren't the bourguise.
Surely you yield more stuff to the crown than a bunch of villages that fend for themselves. Hence +yields. And because the economy and the politics of the state revolve around likes of you (especially if Vassalage is also taken), your domain - a Farm, an organised land dedicated to agriculture, even if it is necessity because agriculture is so horribly inefficent that 90%+ population have to work in fields to avoid mass starvation (which will happen anyway with the next dry spell) - grows in importance to the state. Or vice versa.
Until those pesky merchants amass enough wealth via global trade to take the charge and switch civic to Individualism. Those b*stards.