Until the FCC mandates receivers include HD, the technology will never catch on. The seem to always mandate for TV - UHF tuners, now digital TV - but radio (AM stereo, HD) has never been mandated.
If they were to do HD, it would seem to make more sense to put the money on the FM signals rather than AM simply because of the coverage areas would be much greater. Why, they could even put WSJS's programming on an HD channel of the FM and improve that coverage.
Now that I think about it - wouldn't it make real good sense to move to HD with existing products that already have an advertising base? Just charge a little extra for the HD - help pay for the technology - and begin to build an advertiser base there. With today's digital audio systems, it would be simple to run separate commercials on AM and the HD channel. So, make it a deal you can't refuse for a year or two - make a few extra bucks, and be ready if it ever catches on.