Dang does an amazing job of moderating but I am sure it's near impossible to keep up at this point. At least the overly political article submissions aren't making it through. I've been reprimanded and have learned the error of my ways in comments. Sometimes people just need the reminder. No matter what you are going through in life it's not ok to take it out on others.
I also assumed the same, so I looked back in time. If you read some of the early HN posts, the quality, length, variety is the same as is now. (length seems longer now).
There's even a bunch of "what did this site become" comments from way back too!
I think it's we who change, we mature, grow older, more grumpy or less grumpy.