Mixing records and being a dj is one of those things in life that people assume is far easier than it is. There are many skills involved in mixing your tunes than people think, and it consists of a lot more than just beat matching.
You need to be able to read a crowd - to know what they want to hear next. Not every tune goes on top of another, so you need to pick the right tunes to go together. Then you need to cue up, or beat match to a level where you are confident that the two tunes won't drift apart too much. You need to find a good starting point of the mix, a sequence to start the incoming track where the outgoing track will end a phase at the same time that the incoming track is ending a phase to make it sound really good. With hard trance this can go horribly wrong, other genres are more forgiving.
You need to equalize the incoming tune's levels to make sure it doesn't come in too loud or too quiet, and also that the bass doesn't clash. Then you have to control the mix - making sure your beats stay locked together throughout, whilst fading your track in and perhaps beat juggling a little. Once your mix is finished, it's on to the next one!
There are so many things that can go wrong, and a great dj is one that can avoid them all. A great dj is one that can go for long mixes that fit two tracks together perfectly. A great dj will have the confidence to beat juggle/scratch during a live set. A great dj has his (or her) own style - many people forget this. A great dj is one who can get the crowd to whoop with pleasure after every mix.

What you put in your post does surprise me a little, surely you've listened to many a dj and heard bad mixes? Even people like Dana and Technoboy constantly let beats slip, and if you want to hear truly bad, go download a Scot Project or Kai Tracid set. If all dj'ing truly required was beat matching, then we'd all be dancing to a computer dj'ing in a club.