When people compare speakers, they usually compare them in Direct 2.0 mode, not 2.1 mode. So whether they want to admit it or not, they are also comparing the BASS, which is EXTREMELY obvious to differentiate. They also compare by memory or within minutes or hours or different rooms. But the bass is probably the biggest give away. Next is the localization of the speakers since the speaker are usually NEVER in the same exact spot.
Sometimes comparing these speakers is like comparing the same exact concert from different SEATS.
I think we can tell the difference, but it's not as obvious as you think if the speakers are all equally accurate and you compare them in 2.1 mode (remove bass from equation), switch within seconds, place speakers very close to each other, and sit further away from them.
They may be a lot more shockingly similar than most people think and ever want to admit.
But yes, they can sound different.