Audio components are the size they are so they'll fit with other components. The space hasn't been needed for decades. Most tuners, cassette decks, and cd players have been "mostly empty" for decades, because required circuitry is getting smaller all the time. The only components that still need to be big are amplifiers, because of the heat (and home theater receivers because of all the things that must be plugged into them.
Exceptions are expensive purist designs made with "discrete" components...transistors rather than integrated circuits. HD radios are so incredibly versatile (nearly limitless filter bandwidths and shapes, for instance), because much of their circuitry is "virtual"...it takes place in software. That's a good thing, as a discrete tuner with the processing power of a 200 dollar HD radio would probably cost 1500 bucks, and be huge. Complaining that they're "mostly empty" is the same as complaining because a recording studio is "mostly empty" after multitrack recorders, mixers, compressors, limiters, reverb units, patch-bays, etc. are all replaced by a computer running Pro-Tools, or (my favorite) Adobe Audition.
Software takes the place of MUCH hardware. A good thing, because it makes it possible for us to have "super-tuners" for 200 bucks. Audiophiles know that the level of performance from an HDT1x used to cost a thousand bucks or more. Many who have compared these to Magnum-Dynalab, vintage McIntosh, Marantz, etc...will tell you that the HDT1x pulls in more stations (in analog mode), and that they're quieter, without interference even when there's a 1st adjacent. My cheap-ass little Accurian has NO trouble pulling in an 88.7 rock colid (analog or HD), with a stronger 88.5 and 88.9 on either side. This is super-tuner performance from what was the cheapest HD radio on the market. "Software-defined" radios are a Godsend!
My sync-detector locks on perfectly (analog only, I have no digital AM stations in my area) on my Accurian. It usually takes less than a second, even on weak signals.
