Capital structure (i.e. proportion of debt and equity) is irrelevant in frictionless markets (https://en.wikipedia.org/wiki/Modigliani%E2%80%93Miller_theo...).
That being assumed, management of a company can raise capital by either issuing new shares (equity) or by taking on debt. Given that management is rational, they would issue new stocks whenever they believe the stock price is slightly over-valued by the market and always take on debt if they think the opposite.
But in reality, companies cannot always issue new shares. However, potential creditors know the company could issue shares instead of taking their debt. So, they will lower their interest offer.
Does that make sense somehow?
The total number of Amazon shares has been slightly increasing over the last 3 years [2]. I wonder why that is? If Amazon management believes their stock price is overvalued, it could make sense to issue new shares to take advantage of that.
[1] http://financials.morningstar.com/balance-sheet/bs.html?t=AM...
Maybe stock-based compensation? (I've not checked)
Amazon has, and will continue, upward because they are capable of breaking into new markets at scale. Unlike Netflix which is quickly approaching market saturation, Amazon has virtually unbounded potential to invade untouched markets as they are currently doing with postal and produce. The result is that we can't see where Amazon's revenue will finally plateau. What we do know is that AWS profits make them extremely resilliant to taking losses in these other markets but at the same time highly vulnerable to competition from other providers like Google.
Fyi google has the better product, but it's better because it puts the kind of people who decide which to use out of work. So industry hasn't flipped yet. When they do expect Amazon to take a big hit.