Sometimes it is hard to read intention into a UI without insider-context to know if something is a conscious or unconscious decision. We could very well ascribe valid UX principles to explain why something is a certain way, but it's also quite possible it is more accidental.
Consequently there are two possible answers to your question:
As a conscious design decision, having different margins between elements is an example of using grouping principles to create a relationship between the elements using negative space (as other answers have pointed out).
As an unconscious design decision, it can also be as simple as that's how it looks when you're using CSS margins for flowing lists where you don't know which items are at the first or last position in the row.
The CSS applied to each item would therefore be the same, i.e. margin: 10px; When you have two items next to each other the gap between them becomes the sum of the right and left margin:
download bmml source – Wireframes created with Balsamiq Mockups
The result is more white space between neighboring elements than you have for the first or last item in the row.
With the examples you provided, I would say that the first one looks like a conscious design decision whereas the second example (Netflix) is probably more representative of the cumulative effect of uniform margins in a list.