Hello,
>>Does It makes any difference if I approve the patch made for windows 7 to ALL Groups?<<
It won't be negative impact if you approve an update for Win7 to all your WSUS groups.
Your PC's will install only those updates which marked as needed, so if an update released for win 7 it won't be marked as needed, for PC's with OS version different from win 7. (XP Winserv2003 etc)
So you can approve this update (win 7) to all your groups it will install only on PC's with win 7
Maxim Sinel'nikov