Receivers are priced as low as they are most largely due to demand and marketing! The market is HEAVILY schewed towards "all in one" receivers over separates, and thus all the heavy competition and pricing is going to favor the receiver! Receivers offer the highest overall value(subjective albeit) and features for the money. In a lot of systems, and for most people, I do feel receivers make the most sense, as they have the most too offer at lower to reasonable price points. In short, I think a good clean souding receiver with good inputs and features is all the vast majority of audio enthusiest will ever need!
To be true however, separate pre/pro and amp combinations offer strong advantages sonically over using a receiver. One, the amplifier sections in receivers inherently weaker than what you get from even lesser wattage dedicated multi channel amps! Receivers amp sections tend to be somewhat compromised in comparison. A receivers power supply has to drive many things, including the amp sections, the processor, the displays, the preamp section, the processors, etc. You couple that with all the limited space, compromised electronic issolation and interference, etc, and you'll ALWAYS FIND that a receiver simply can't pump out the clean high current juice like what you get from a descent power amp! Also, the preamp sections in receivers tend to be softer dynamically, not quite as tight and refined sounding, with less channel separation, higher signal to noise ration, etc. You couple those factors all together and the sonic differnces add up!
Still, the biggest factor in difference is in the amplifier section. If I had to use a receiver as a pre/pro, I'd be much happier with a clean receiver as the pre/pro section, and use a dedicated outboard amp to close the gap!
Also, to be fair, using "powered speakers" or configuring your speakers as "small". and/or using a dedicated powered sub for all your bass dubties helps the receivers amplifier sections TREMENDOUSLY! Taking the heavy demands off a receiver's amp sections(already challenged using "Passive" speaker crossover networks and designs instead of "active's") gives the receiver's amp's MUCH NEEDED HELP INDEED!
Another thing I've also noticed, still, is that the receivers processors keep getting better and better, and the techonology as a whole keeps moving up and up! Receivers sonics on the whole have gotten much more competetive with good separates "front-ends", and this makes the choices that much harder..but better for us consumers!
I would think, considering what the average HT/music enthusiest would likely want/need for his money, that a modest price receiver still will be all most will likely need! With proper set up, possibly some "powered-tower's" and "active subwoofers" in-toe, I doubt most will go wrong with a receiver as their "hub"!
