False.

[2:11pm] 8 [/usr/local/bin]:server% tar -cvf /tmp/lie.tar /var/tmp/has
+h
a /var/tmp/hash 5K
[2:11pm] 9 [/usr/local/bin]:server% cd /tmp
[2:11pm] 10 [/tmp]:server% tar -xvf lie.tar 
tar: blocksize = 12
x /var/tmp/hash, 4286 bytes, 9 tape blocks
[download]

For example this was run on solaris. It is very possible to have fully qualified (non relitive) paths with tar. and _most_ unix flavors do this by default if you specify the absolute path while creating the archive (without the chdir option). In fact most versions of the tar the comes with Solaris make it impossible to extract relitive when the files are stored absolute -- your two choices are really to use gnu tar (which lets you ignore absolute) or chroot to the location besides root that you wanted to untar to.

-Waswas