What do the application icons in the upper-left hand side of the notification panel mean?
OK, I figured out, those icons do not correspond to which applications are running,
but rather, to those applications which have awaiting new information for the user.
When the user drags the notification panel from the top of the screen, those same
icons appear next to the name of the application sending the notification and the
message posted by such application also appears next to the application name in
the list. This should answer the question.