ok, say I'm using DS18S20 instead ... the "problem" remains 
Say, I have ONE that measures 20.5° when then true temp is 20 - the DS18S20 is inaccurate at the same level as the LM35. Means, that I have to live with the inaccuracy. Say, I get a second one and that one measures 20.4°. Doesn't help me much, does it?
But if I, out of pure luck, get two and one measures 19.5 and the other 20.5, how sure could I be that the true temp is something like 20 +- less than 0.5 ?
BTW: can somebody tell me why DS18S22 is more expensive that DS18S20, though the 20 is MORE accurate? 22 offers 12 bit conversion, but what does this help if the inaccuracy is larger anyway?