(I guess they assumed that the fitter riders bought the high end bikes, unlike today)
Although 13-30 often came with 28/38/48 rings so actually had generally higher gears
Manufacturers are silly.
As has been said, 12-28 is the "classic". That 12-21 is a road cassette really but no reason you can't use it if you don't need lots of range. Does depend what rings you're using, of course. 11-28 7 spd is a bit gappy in the middle but that may not bother you.
I used to use 24/36/48 with a 13-30. FEEL THE LOW GEARS.
_________________Behind Bars: Collected Mountain Bike Articles ebook
- contains significant retro content