From what I've been reading, in GA airplanes, Vno or the top of the green arc is a speed at which the aircraft is able to withstand up or downdrafts of up to 30 feet / second without over loading the plane
Most of the light aircraft we fly today were certified under the old CAR part 3 regs (pre '65). The certification criteria dictated that when operating in the green arc, the aircraft structure had to withstand an instantanious '50 per/sec vertical gust without bending anything. That's around 30 knots. I reckon if you happened hit a vertical gust of this magnitude whilst punching along at 160 kias in the 210, it'd certainly capture your attention quick smart. I've got absolutely no doubt one would be looking out the window at the wings rather suspiciously (mistakenly as it turns out).
When in the yellow arc by the way, the airframe has to be able to handle a '30 per/sec vertical gust, again without bending/breaking anything.
Another misconception that you quite often hear, is that it's OK to descend at cruise power in smooth air with the IAS in the yellow. Inncorrect.
The regs (CAR 3) state that the yellow arc is only for inadvertant excursions of airspeed . In other words, if you find yourself on the high side of Vno, get yourself and the aircraft back in the green arc on the ASI.
The C210 is deliberately limited by Cessna to avoid overstress in the un strutted wing/fuzelage attach area.
This has been the subject of debate for years but the end conclusion is that the way the wing attaches does warrant care in turbulent conditions.
The C210 was limited by Cessna (as was any other model manufactured by Cessna) to meet the requirements of CAR 3 under which the aircraft was certified. To say that it was hobbled by Cessna because the wing was strutless or because of the way that the wings attached to the fuselage is incorrect. The strutless wing easily met the requirements needed to gain certification under CAR 3.
The wing on the 210 when compared to say, an A36 or Saratoga/Lance, doesn't warrent any extra consideration other than the normal precautions that a pilot might take when operating in turbulent conditions.
The fact of the matter is, the spar carry through structure on the 210 is stronger the the strutted wing of the 206. So if you do happen the hit that 50' per/sec gust in your 210, relax.
As an aside, one of the strongest set of wings that Cessna ever put on aeroplane were strutless. These belonged to the 195 series. Because of a number of design considerations that were made at the prototype stage, the wing was overbuilt (not on purpose) i.e. it was heavier than it needed to be.
When Cessna tested the wings, they didn't break when they were supposed to. They went way, way past the point at which they were supposed to let go. So rest assured, when out driving in your 195, you'll break before the wings do!