I think this is the point. I can immediately tell what these posts are about via the image without having to read anything. I can then read the details if I want. Also, If G+ is anything like Facebook one of the most shared content types is photos so it makes sense to prioritise them.
>> Third problem, the lack of discipline in using the whitespace. Whitespace is one of the most powerful, visually pleasing and least intrusive way to bring orders and visual hierarchies to a design. Yet what do you think of the whitespace in this Best of #Python page?"
This seems like a bad example. Normally that whitespace (the link) would contain an image and some text previewing the link. They just couldn't parse it from the webpage. In this case the OP just picked an example to fit his complaint.