Wall Street still keeps their stock price up because of rising revenues so Amazon can borrow money with impunity to make up for these losses. This allows them to keep dropping prices even when they are losing money. A small company cannot do this.
Sure they can, though likely they will do it through private equity, not Wall Street. The problem is that few small companies know how to dramatically increase their revenue by creating new industries like cloud computing, and reselling sunk costs like external fulfillment.
It isn't hard to raise revenues when you don't have to care about profitability or cash flow when setting your prices.
Do you really think Amazon doesn't care about profitability or cash flow? Do you believe their business model is, "Fuck it, sell it at a loss, Wall Street will bail us out?"