Actually your classical HD-3 argument is a good reason for pushing HD. When HD radio becomes universal (and I can hear your teeth grating), then the NPR stations can swap the channels around and put their news/talk on HD-3 and classical back on HD-1 :-)
Or, alternatively, since NPR saturate the non-comm band almost as much as Christian broadcasters, they could actually get together and cooperate with nearby NPR stations on what programming they will air, instead of having the same exact thing on five frequencies like I have heard on occasion. Do they operate in a cooperative or a competitive mode?! It is as bad as Christian radio, where several frequencies carry the same translated station, or all play the same hum-drum boring type of preaching and suckish music. Cooperation - something the Christians never do - what a concept if NPR could do it! Even a conglomerate that owns several stations in a market knows to program different formats on the stations they own instead of the same thing on all of them. Why not NPR?
Easy answer first: "Why not NPR?" Because NPR is not a radio station operator, it's a program provider (and only one of several program providers, at that) to nearly 400 local stations around the country, which make their own local or regional decisions about what to carry when.
As you might expect from local stations, the level of cooperation varies widely. If you're in Louisville, Kentucky, you're lucky enough to hear a wonderful example of cooperation - after competing with similar programming, the public library-owned WFPL/WFPK and the U. of Louisville's WUOL got together a while back and formed the "Public Radio Partnership." While the library and the university still hold their licenses separately, the stations are operated cooperatively with joint studios and management. WFPL does news/talk and jazz, WUOL is all-classical and WFPK is a great AAA station.
Or perhaps you might be in San Francisco, where the public schools' KALW competes with KQED (owned by a community nonprofit). Both do news/talk - the classical niche in town belongs to commercial KDFC - but they have very different program lineups and surprisingly little audience overlap.
In other places, the rivalry is stronger. WBUR and WGBH in Boston are about to go head-to-head with news and talk, though we don't yet know what WGBH's program lineup will look like. In some areas, there's simply a lot of overlap at the edges of regional networks - in the Champlain Valley in northern NY/Vermont, most people can hear good signals from Albany-based WAMC, the northern New York "North Country Public Radio" regional network and Vermont Public Radio's two networks (one news/talk, one classical). There's a lot of duplication of national programming among the three networks, but also a lot of differentiation in the focus of the local programming surrounding the national shows.
Two more points: first, I know of no public broadcaster that's doing classical on an HD-3, though I know of many on HD-2. I'd be interested to know of any classical HD-3s out there.
Second, for every WRNI that's being hammered badly by incoming interference from adjacent-channel HD signals, there's a WXXI in Rochester, which is heavily promoting its HD-2 (on full class B WXXI-FM 91.5, which is all-classical on analog/HD-1) as an alternative source for the news/talk programming on WXXI(AM) 1370, which suffers from a 1940s-era nighttime DA that misses half the population growth in the market. At WXXI, we just wrapped up our pledge drive, which set a new record for both total money raised ($278,000 against a $275,000 goal) and number of members who donated - and one of the most popular pledge premiums was the Insignia portable HD radio. We'll see what the members have to say when they get the radios. They're never shy about telling us what they think.
(Usual disclaimers: I speak only for myself and not for WXXI or any of my other employers.)
