Perhaps I'm missing something as well, but having the for loop iterate over the results of 'ls -l' doesn't seem like it'd work, as it would try to untar things like '-rw-rw-r--' and 'Oct'. Perhaps 'ls' would be more appropriate. Heck, you could even leave the external program out of it.

for file in *tar; do tar xvf $file; done
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thor