Houses were built like that for many years before the hangers even existed. The ends of the joists are sitting on top of a heavy beam, so they aren't going anywhere. Additional blocking or cross bracing mid span makes the floor even more stiff, by spreading the point loads over several joists at a time.
Pretty standard practice - these days and prior. I MUCH prefer bearing joists on a drop-beam like this vs. flush or side-mounting w/ a hanger, or a ledger. Not always possible w/ low clearances, but a much more stable configuration not relying directly on fasteners.
Yes, This is a very common practice. On the west coast where about 50% + homes are joist floor this is/was the standard code requires max 8 ft for blocking. Sometimes seismic will require blocking closer than 8 ft and will require some hold down straps the look like a hurricane tie but wider.
Hangers facilitate shorter joists, basically trading wood for steel. Done well, there's really no structural difference, but we always check the correct size and count of fasteners (nails or screws) have been used so there's no worry of failure down the road when the wood dries out and shrinks a little. Given wood prices these days, this framing with more wood and less steel is economically a surprising choice.
Looks like the drop sill is a little low for code, and I wonder what the HVAC guy is going to do about his duct work? Probably put it all in the attic. They just need to be sure the subfloor joints are fully supported with a scab board if the joint doesn't fall on the lap where they can stagger the plywood. I assume they are using plywood. With the prices the way they are now, they may revert to diagonal 1 x 6 sheathing..........