Technically yes but not as detectable by the human ear, or perhaps the effect is not as pronounced at higher frequencies. The decrease in bass response is much more noticeable. Easy enough to try if you have banana plugs on your speakers (and turn off the sub).
I've never researched this. If all sound was affected equally, then you would simply get a lowering in volume at all frequencies. That's not what you hear though when two speakers are working out of phase. It's most noticeable in the bass. The more I think about it, I suspect that it has a lot to do with the fact that half of what you hear in a room is reflected sound that arrives at the ear at different times, so the reflected sound (mostly mids and highs) will not get canceled out in the same way as low frequencies. Two speakers outdoors or in an anechoic chamber might behave differently. Any sound engineers out there with a proper explanation?