It's my understanding that the order displayed in your journal is determined by display time, but the order displayed on the reading page is determined by system time. I'll check this later.
Regardless, your initial objection, while valid, wouldn't be a change from current behaviour as new posts that slip in between existing posts are going to be missed by most people (say I read entries 1-20, while I do this someone posts in a way that would appear at entry 10, when I click back, I'll currently read entries 20-39, if I go back to the top later, I'll read down and stop at what was entry 1-it's that that leads me to think Reading goes of server time anyway, and if it doesn't I think it should)
no subject
Regardless, your initial objection, while valid, wouldn't be a change from current behaviour as new posts that slip in between existing posts are going to be missed by most people (say I read entries 1-20, while I do this someone posts in a way that would appear at entry 10, when I click back, I'll currently read entries 20-39, if I go back to the top later, I'll read down and stop at what was entry 1-it's that that leads me to think Reading goes of server time anyway, and if it doesn't I think it should)