Also, when you apply for a travel visa in China, you have to tell the government exactly where you're travelling within China (e.g. x days in Beijing, x days in Shanghai), and who you're going to stay with (names, addresses). It's designed to prevent foreign journalists from digging up dirt, especially around election years (they increase the visa fee and make a double entry visa more awkward during these times, so journalists travelling between mainland China and places like Hong Kong will find it more difficult).
#2. Yes, they ask for that but they don't check. The AU, NZ, RU, UK and US authorities also routinely ask for a travel itinerary.
You will have produced at the very least one address you'd be staying for the first night in the country you just landed on. You might have been asked further plans at border control, especially if you are not white.
China does a lot more , a lot worse, that is in no way "optional" for citizens or travelers alike
I am a Chinese citizen who has NOT been required to submit my social media accounts (US ones: GitHub, twitter, Facebook or Chinese ones: weibo, renren) to the Chinese immigration in the past. And to my best knowledge foreign travellers are also not required to do so. I can also imagine the story will blow up in every news media if they start doing so.