I think there is a significant (although not a majority) group of people (especially in terms of high end SPS/Acros) that believe that natural live rock (or very, very, mature/established dry rock) has some inherent benefits that make it easier or more successful in keeping these more challenging corals prosperous. I think the general theory is that live rock has numerous other components to it other than nitrifying bacteria and because of this a simple cycle and fish does not make dry rock a suitable equivalent. As tanks with dry rock mature the ecosystem (for lack of a better word) begins to fully diversify and bring in the necessary environment for these higher end corals to really thrive.I agree that the use of porous rock that contained huge amounts of denitrifying bacteria greatly advanced the ability to keep a low-nitrate tank. There is a lot of 'speculation' as to the other stuff on 'live rock' that was supposedly beneficial - but I'm not sure thats true - and if you buy a little live rock you can build up the benefits.
The reason (I thought) that people changed from live rock to 'dead rock' was 1)Difficulty in the curing process, 2). Hitchhikers, 3) Cost, 4) Dead rock seemed to work as well if used properly. I do not understand the logic of saying dead rock is causing a problem - unless you can definitively state what the 'magic ingredient' in Live rock is that is causing the dramatic benefit. IMHO using cured coral rock with everything 'killed' by whatever method - is the equivalent of 'live rock' that has been cured wet.
If by 'dead rock' you are talking about 'man-made' rock of various substances, Im not sure these are as successful as natural rock
Now... I don't think this is necessarily true or even something you can easily quantify as I had to be rather vague just describing the school of thought. However, surely the live rock from a well aged, very well cared for tank is going to have SOME benefit to it over bleached dry rock that has been introduced to a sterile new system that is 6 months old. What specifically? I'll let someone with more expertise tackle that.