Norton AV Dual Protection or Norton AV 2011 for Windows?

  I'm trying to figure out which product I need.  I have Windows 7 installed on a Boot Camp partition on my new iMac.  I want to run Windows anti-virus software.  I do not really think I need AV software on the Mac side, although I'm willing to be educated.

 

  The Dual Protection product offers both NAV 2011 for Mac and NAV 2009 for Windows.  Is there some reason I shouldn't just buy NAV 2011 for Windows and get the most up to date version, given that I don't really want the Mac product?  Why wouldn't the Dual Protection product include NAV 2011 for both platforms?

 

  Thanks!