Economics of Time Allocation

The top-posting "problem" is due to issue of time allocation
Although you've seen the quote before in most cases, to be sure you've seen all the new material in this message you must read to the bottom of the message, which takes time and effort
- In accounting, "reading to the bottom" would be called "overhead"; this cost is like a lump-sum tax. It is born by all readers of the message, and is like a congestion externality
Do you have to read to the bottom?
- This depends on whether you expect new information to be added by the author of the current message farther down in the message