"Why do some topics have [view all] next to the subject?"
When a topic contains too many replies, it can take a long time
for your browser to download the entire file. This can be annoying
if you've already read most of the messages in that topic.
To overcome this, a topic will automatically switch into
the auto-sensing mode when then number of replies exceed certain
number set by the administrator. In this mode, you can view
one message at a time, thereby eliminating the need to wait for
th entire topic to download.