I cant believe that this hasnt been brought up yet.. Some of them may take advantage of the sync benefits of a dvs system with the CDJS. I've seen a couple of "big names" use CDs, yet have the pitch identical on each deck the whole set. If one moved, they moved the other when they put in the next disc. Its not all that difficult to have their music pre set to a specific BPM. Now its easy to mix with 4 cdjs, as well as use cue points. the only things they are missing is the per deck effects, which is really overkill for the most part.
I love my traktor/4D setup, but i do miss actually beat matching from time to time.
I like the "walking on a tightrope" feeling while keeping tracks in sync. There is more of a gratification when you synced the tracks. And even tho i sometimes go a few months or more without using my 1200s or cdjs, i find that gridding tunes in traktor keeps the ear keen for beatmatching. I NEVER have an issue beatmatching when i walk up to a set of decks.