No, stock markets do not perform the same function as grocery stores. Grocery stores take on inventory risk by purchasing (in bulk) the goods that they think they can sell. If their inventory goes unsold or spoils, they lose. Stock markets provide a _venue_ for trading, but it is the market maker which takes on the inventory risk. An appropriate analogy would be that the grocery store is renting from a separate property owner. The property owner collects rent from the grocery store, just as stock markets collect "rent" (trading fees, colocation fees, system access fees) from market makers. In both cases, the inventory risk is managed by the middleman (grocery store, market maker).
That's a pretty weird example, because that is the _only_ stock that trades at $200,000/share. Such a high price forces away liquidity intentionally, because the capital requirements of even 1 share are larger than most futures contracts. For most individuals it is more like buying a house than a stock! As a result, there is a NYSE employee (I forget the title, maybe DMM?) on the floor which _manually_ matches buyers against sellers. Other exchanges I believe still match electronically.
Aside from that, how does your statement relate to inventory risk? Market makers and grocery stores take on inventory risk. An absence of market makers in BRK.A* would only show that nobody wants to take on that risk. It does not change the role of the exchange. Exchanges facilitate matches, they are not a counterparty.
Yes, and in order the markets to perform this function they needs lots of active participants with differing investing time horizons. Without market makers markets tend to be very inefficient at their job.
