I find this a fascinating question.
To me, a kit is the ENTIRE kit. It's my instrument. ALL of it. The cymbals are part of it.
Take a saxophone. It's a saxophone. If you take away the mouthpiece, it's not a saxophone. It can't make saxy noises.
Same thing with a drumkit. If you take away the snare or the cymbals, it's not a drumkit. It can't make drumkit noises.
Pedantry aside, I don't think there's anything wrong with buying "cymbal sets". I think there's a bit of a prejudice against cymbal packs and matching snares on these forums. ;-)
As another poster noted up-thread, some brands - like Paiste - are predictable. An 18" Signature Fast Crash will sound like any other 18" Signature Fast Crash. To my ear, most Meinl cymbals are the same way. Must be that Germanic "alles in Ordnung."
Cymbal packs are - presumably - matched to work together, to blend musically. That's important. I dread adding a cymbal. I won't know if it blends until I get it home. That sucked when I lived 15 minutes drive from a decent music store. Now that totally SUCKS. You guys complain about not having a drum shop nearby? I can't drive to one. At all. Period. I have to fly or take a boat. If Tambu in San Juan, PR doesn't have what I want, it's 1,100 miles to Miami.
That's why I <3 sites like
www.Mycymbal.com where I can actually hear stuff. I still don't know if one particular cymbal will blend with my existing plates, though, so I only look at sets. I lust after
this Bosphorus set, but I'll probably end up with the Paiste PST7 set further down the page.
Anyway, my point is that there seems to be an understandable bias against cymbal packs. Understandable given that personal preference dictates - you may not like the ride in the pack, etc. I don't think that bias need be applied as broadly as it is. Yes, cymbal voices are individual. But you know what? So are drums. Some of the same drummers here who wouldn't dream of buying a set of cymbals also wouldn't dream of putting together a "Frankenstein" set of toms and bass(es). That's inconsistent. If the sound is so important that you'll mix and match cymbals - don't forget snare drums! Can't use the one that came with your toms and bass, nope, that won't do at all! - then insisting on uniformity in your toms and bass just doesn't make sense.
Anyway, I think this essay was fueled by too little coffee too early in the morning. Still an interesting idea. ;-)