I haven't given tuners much thought because I hardly ever listen to FM radio, and listen to AM radio only when certain talk shows are on. But, if there is a measurable difference in quality between tuners of old and those of new, I would surmise that it is probably due to increased emphasis on other receiver/stereo elements such as Surround Sound, matrix decoding, DSP, XM/Sirius, and all other sorts of "goodies" you get these days. So yes, it would make sense to me that a standard AM/FM tuner in one of these systems
is probably an afterthought - thrown in there for the 10% of the people who actually still care, and because Frequency and Amplitude modulated radio waves are still buzzing about our heads. So, less time/energy/cost/research goes into the newer tuners as a result. But they're still there, they are still able to perform, and I have yet to hear anyone complain about theirs, be it a seperate or integrated.
Standard radio is antiquated and on the verge of becoming obsolete, IMHO. People want their "On-Demand" media, via iPods, Satellite Radio, media servers, streaming, whatever...