Agree about the difference between 9.8 and 9.6 being miniscule, and usually not worth the big jump in value common between 9.8s and 9.6s.
However, regarding ASM300, there are almost 3x as many 9.6s as there are 9.8s. For comparison, another popular CA key like NM98 has only about 30% more 9.6s than 9.8s. So basically a 9.8 ASM300 is significantly "scarcer" for being a major CA key, which may be a factor as to why ASM300 9.8s are almost 3X the price of the 9.6s while NM98 9.8s are only about 2x the price of the 9.6s.
ASM300, it's a tough cover to get in 9.8.
Good point made, I did not look into the census before I made my statement, but good to know. With any black cover comic book, getting into the uber uber high grade 9.8 and up is tough! I guess it makes sense why 9.8's sell for so much. I remember the days not too long ago when 9.8's could be had for under a grand. My friend actually was on the verge in buying a 9.8 copy that time for $900, but backed out. Boy he regretted that so much and is kicking himself to this date.