High share price does not equal "bubble". AMZN is sort of a special case, but GOOG and APPL both, in addition to being debt-free and sitting on lots of cash, have very low PE's and decent growth prospects. One can argue proper valuation, but neither would be considered grossly overvalued, certainly not "bubble" prices.
SNE on the other hand...well, its ugly. Growth is down, debt is high. Prospects are limited. Shares go down. Then, the shorts jump on board and ride for awhile. Eventually, it will recover a bit and we'll see if they can figure out a way to turn it around. Not too soon, I hope...I'm on the short side, at the moment. I had a bearish option play going on and the options got exercised on a small recovery. So, I ended up short shares...I didn't see any reason to close out the position and I still don't, for the near term.