Even for blogs it might matter if they are talking about breaking news. A timezone can roll a date forward/backwards one day.
I am talking about having a UX date/time standard for all of UX, not just blogs.
There is UX where knowing timezone is critical, ex: when analyzing logs, breaking news etc.
To keep things simple it would be great if everyone agreed to always attach TZ info to any date or time shown.
Furthermore, any blog/article that might not appear important at the time it's posted, might become important DUE to breaking news. So just put timezones everywhere an be done with it :)
Genuinely curious as to why knowing the timezone instead of approximate date matters so much.