Not totally true. On the PX-716, DVD+RW uses the booktype set by DVD+R (it has done this since fw 1.01). In fact, some earlier versions of recording packages incorrectly checked the booktype instead of the media type and wouldn't allow you to erase once it is set (but this is not a problem any more).
 I suspect that maybe zevia and G@MEFR3@Ks info was due to settings in Nero itself, not Plextools. Also, I haven't tested the bitsetting in firmware 1.03 yet, but I have some Sony DVD+RWs that were bitset by firmware 1.02.
DVD-R/RW can be theoretically changed also (see http://www.cdfreaks.com/article/150 under DVD-R bitsetting), but I haven't tested this on my PX-716A and don't expect that it is supported. If it were, I would suspect that it, too, is using the DVD+R option setting value for this.
[2nd edit] It looks like, at best DVD-R "bitsetting" belongs in scare-quotes, since it is a bit of a hack and contrary to the specification.