"The goal of the GNU GPL is to ensure that all users have the
four essential freedoms--(0) to run the program, (1) to study and
change it, (2) to redistribute it, and (3) to distribute modified
versions. Access to the source code is essential for freedom 1 and
freedom 3. Thus, we designed the GNU GPL to insist that all
redistributors make the source code available to their users. This
requires them to do a little extra work, but that work is generally
necessary for the sake of the users' freedom. Keeping source code
conveniently and reliably available for the users is more important
than saving distributors a little effort.
"Under GPL version 2, distributors who release binaries through
a network server have to release the corresponding source code in
the same way. This requirement is the only way to assure that users
can get the source, and the that it is the right source..."