well.. price now plays a part, in australia, I can pick up a A05 for around $550/600 AUD, where as the Sony DRU500a is around $900 AUD...
in my opinion +R/RW isnt worth that much considering all ill use that format for is PS2 games, even then, my PS2 reads -R/RW as well...
and probably down the track, as prices drop, and it turns out that +R/RW has something so esspecially good that everyone MUST have one, im sure i could pick up a seperate +R/RW burner..then ill have both types
oh well...you know what they say, different strokes for different folks