Is trading in the commodity futures much more riskier than trading in stock market futures? My understanding is that the price of a stock at the stock exchange is determined by supply demand mechanics during trading hours, and the price of futures is determined by the price of the underlying stock. In effect its the price of the underlying stock that controls the price of the future(Black–Scholes model) The price of the stock-future is strongly coupled to the price of the underlying stock price.

Consider the commodity exchange where the  futures price of a commodity is determined by supply demand during trading hours and is not directly determined by the real price(current price of commodity available to the public).

Contrast the scenario at the stock exchange with that of the commodity exchange. As an example, if the current real price of copper is Rs 340 per kg in the shops. The price of the copper futures is in no way directly determined by real price of the commodity the way the price of a stock-future is determined by the underlying stock. Hence the futures price of commodity is weakly coupled to the real price of that particular commodity. Hence it may be said that the price of commodity futures is much more volatile/speculative in nature than price of a stock future. Correct me if my understanding is wrong.
Let's start with the statement - 

'Consider the commodity exchange where the futures price of a commodity is determined by supply demand during trading hours and is not directly determined by the real price'

first, this statement is not accurate. Not everyone that buy a commodity future ever intend to take delivery. 

Second, you need to look at financial future vs. Physical future. Most of the time they move in tandem (correlation nearing 1). However, near delivery, they become less correlated. In fact, physical commodity carries delivery risk. If you have not disposed of the future in time, you'll have to take the delivery. In that case, you have to deal with storage cost. 

This leads to the third point - convenience yield. Hard to quantify, hard to hedge (unlike stocks or other financial instruments) - where would you store 1MM barrels of oil today? At what cost?

Last point is - what is 'real price'? The cost of producing a barrel of oil? 1 ounce of gold? If so, how would companies (and in turn their stock) profit? 

Now, to the question itself - to truly assess whether commodities are more volatile then other financial instruments you have to define several parameters including observation period, asset classes etc. If you don't you cannot make a proper comparison.

Finally, Commodities post 2009 - part of the drop in commodity prices could be attributed to the fact that due to costs and regulation banks are not such big participants in the assets as they used to be. Here, you could say that 'lack' of interference is simply bringing prices to where supply and demand dictates.

Now, compare all of the above to recent price drops in Twitter and Linked in stocks. With that in mind, Commodities look 'stable'...