Operating systems bridges the gap between hardware and application software?
Before computers were connected in a network, the answer to your
question would have been "yes." And it is still true that Operating
systems communicate directly with hardware.
But life is more complicated now -- there are additional
"layers" between the application and the hardware. For example,
there might be a communication layer "above" the operating system,
which helps application programs on different systems communicate
with each other over the network. Or there might be a database
layer, which also sits between the application program and the
OS.
The purpose of these layers is to let you change the underlying
parts of the software system without having to rewrite
applications. For example, a database layer lets you change the
database (say, from Oracle's 11g to IBM's DB2) without changing the
application. Similarly, the communications layer lets you change
the hardware and the operating system "underneath" the
communication layer, while allowing existing application programs
to operate as before.