No, it doesn't, you're right! The webcam app doesn't do sound; the giveaway is that there is no configuration tab for any sound device!
Other applications, such as Skype work fine with the internal mic, but if you want to check your mic is working first, start a terminal and do
arecord test
then talk a bit, then hit CTRL-C.
Now do
aplay test
and you should hear your voice coming back.
Clean up after the test by doing
rm test
as the file you've recorded might be quite big!