The vines you see are almost always for show.
I have worked in Sonoma Napa and Mendocino, that is absurd. They do buy some grapes from out of the region but the ones in those vineyards are absolutely not for show.
freedumb2003 didn’t say the grapes in Napa & Sonoma were for show, he said the vines at wineries were mostly for show. I grew up in the Napa Valley - I know a lot of winery people, vineyard families, and vineyard management folk. Some wineries have no real vineyards of their own - they buy grapes from local growers. Some wineries own acres of vineyards but also buy grapes from local growers. A few wineries use only their own grapes.