To bring this back to class again, having everyone in identical gear gives away the fact that they don't own this stuff anyway, which, if you're a bit of a snob, may not be a signal you want to send. In England, every upper middle class man is expected to own a morning suit (if you don't you rent one without telling anyone). Thus at a wedding, you simply tell people to turn up in morning dress and that's what they do - naturally they'll all be similar but none identical. If you want to identify the bridal party you perhaps have matching boutonnieres.
Compare these guys who clearly own the stuff (literally and metaphorically, if you know what I mean) -
and these guys, who clearly don't -
Same thing applies to lounge suits.
Remember that not so long ago (fifty years or so) there were no such things as matching suits period, as there was no such thing as an OTR suit. Everyone either went to a local tailor/seamstress and had clothes made, or they bought second hand clothes that had been made for someone else. Either way, it was all unique.