I think that most people in a club are totally satisfied with a DJ who can effectively fade in and out from one song to the next, and that takes little to no talent. That would not get me booed of the stage.
And mixing a beat into the existing song is a matter lining up the beat and only happens for 15 seconds or so. That's not really a musician to me.
Even just within the beatmatching / dance type of DJing, there's more to it. Quite often people will listen to a techno record, and say 'huh, that's just a bass drum going 4 on the floor'. And to some extent they are right! A lot of club records are not 'finished' pieces of music - they require the DJ to cut them and mix them together with other tracks to create the whole performance.
An example :
I don't actually like Jeff Mills' mixes that much, though I do love some of the albums and tracks he's produced.