'is not' filter condition

[goatee]

Let's say, you want to select everything but holiday music, and no live recordings. Okay, let's try:
Occasion is Background,... (all except holiday) AND
Quality is Excellent,... (all except live)

Great, looks good, right? Unfortunately, the music without any quality or occasion set, are left out. (And new occasions and qualities added later are also not selected). So lets try to fix that...
Occasion is Background,... (all except holiday) AND
Quality is Excellent,... (all except live) AND
Occasion is unknown AND
Quality is unknown

uhh, error occasion cannot be set AND not be set at the same time... let's try OR: you now have music INCLUDING holiday music of unknown quality and live music of unknown occasion.

If we now, for instance, introduce an 'is not' filter condition:
Occasion is not holiday AND
Quality is not live

no holiday recordings, and no live recordings. Need anything else? Nope...
And since there is a "doesn't equal" condition for 'Type' and a few 'title' options containing "doesn't", and maybe a few others, you'd expect an 'is not' condition where 'is' also applies.

Is there any (good) reason why there is no such condition yet?

[Lowlander]

Already requested: http://www.ventismedia.com/mantis/view.php?id=6360

Workaround is create a AutoPlaylist with Quality equals Live and then another AutoPlaylist where Playlist is not that first AutoPlaylist.