A strange trend I noticed: critical China news tend to pop up close to 9:00 EST, and at 9:00 PST positive China news tend to pop up, and negative ones get buried.
It's all about when large masses of HN users show up at work, check their email, get their coffee and post on HN and the demographics/opinions/ideology of those users. If you make a comment that is critical of SV (and SV's definition of "critical" is highly inclusive) or doesn't take the official California compliant line on some political issue when you're on lunch break on the East coast you're gonna get down-voted hard. HN users on the west coast might be slightly more pro-China than the east coast and you're noticing the effects of that.