@Justinian
The decline in the stock price reflects a decrease in the valuation of the assets that Sony possesses. The market will determine what a asset is worth based upon how much it would sell for in the existing market. Right now given the fact that Sony cannot make a profit on many of these assets it is a logical deduction that nobody else could either. So the demand for these assets would be low on the open market.
Assets do not have set values. Only what others are willing to pay for them. Most of the value in these assets are in as is condition. There may be potential in them for a buyer, but not necessarily in the as is condition. A factory that makes televisions may not be able to be sold as is. Maybe only the building will have real value to buyers, and the machinery may need to be sold as scrap, or at a fraction of its cost. A intellectual library may only be valuable enough when it comes to a few songs, movies, or licenses. While the rest may be viewed as worthless.
Obviously when a asset makes money then it is good as is, but Sony doesn't have a lot of those. Investors really aren't believing in what Sony is selling. They don't believe that the majority of these assets can be used to actually make money, and as a consequence aren't worth much money. The investors are probably right. Sony had more then enough time to demonstrate that it could make a number of assets profitable.
That all said this isn't actually the big problem. The resale value of assets directly I mean. Sony has enough actual liquid assets in the form of cash to cover operating losses for some time. The real problem is that Sony leverages their assets when negotiating interest rates with lenders to finance investment, and the day to day cost of actually doing business. When the market devalues the company, and by extension the assets of that company. It makes the company look like a riskier proposition for lending.
So Sony which is used to getting preferential interest rates from lenders. Will probably have to pay higher interest rates on their loans. Which is going to hurt the bottom line even more. Sony could dip into its own liquid assets, but that may hurt the stock further, and those liquid assets are part of what Sony would use to negotiate loans in the future. So in a very real sense the stock dropping in price is going to hurt the bottom line at Sony. Probably forcing the company to scale back on future investments.
As far as this forum is concerned this could lead to the PS4 being a weaker platform, because Sony will not be in a position to invest as much in its development and manufacture. Remember Sony had taken out loans, and sold assets equaling up to about two billion dollars prior to the launch of the PS3. Higher interest rates, and the lower value of the company as a whole. Will probably see a substantially smaller upfront investment.