So tptacek is correct that a farm inside a grocery store does not solve grocery affordability for the poor, because the problem is due to transportation/access, not the cost of the goods.
The bridge between these two views would maybe be if there was a solution of vertical farming that used little real estate and was able to set up a vertical farm in a poor area and had minimal real estate footprint/low rent costs.
Paper on Food Deserts in Chicago (or just google "food deserts chicago"): http://www.usccr.gov/pubs/IL-FoodDeserts-2011.pdf
I'm not sure if you shop mostly in Whole Foods or buy individually plastic-wrapped bell peppers at Trader Joes, but go to a Mexican grocery store some time and fill a cart full of green things. Vegetables are very cheap.
You might think it is for marijuana but you miss the point. Self suffiency is something we should strive for, we shouldn't be dependent on other places for food or shelter or water, we should produce those things locally.
If you think ahead even more, this is important for space travel and colonizing other worlds or even different parts of the world.
This should be an open standard and shouldn't be something people can't afford. This could change how people get food and drastically adverse the effects of being in a food desert.