From the standpoint of purely production costs, there is little reason why they would make them different. It adds costs with no practical net gain other than stocking more parts.
ftp://bama.sbc.edu/downloads/national/hro50/
ftp://bama.sbc.edu/downloads/national/hro60/
These are the online manuals for the two radios, and if you want to compare the schematics this should answer things.
: Can anyone tell me if the National HRO-60 plug-in coils
: will work in my HRO-50t?
: Thanks for any info.
: Gerald