I've played hundreds of hours of Hardcore Diablo II, and hundreds of hours of normal Diablo II.
Over the last couple of years, I've gotten to know several other hardcore Hardcore players, if you know what I mean. Every single one of them plays a ton of normal in support of their Hardcore characters. So do I.
I'm sure that it's not a requirement, but I find it very important to spend 50% or more of my time learning all the tricks of the game in normal mode as a preparation for preserving my Hardcore character(s). Just learning about and knowing what near-death is like, and being very familiar with the bottom of the health globe is something that a serious Hardcore player will only do with normal characters.
I learn the tricks.......on Hardcore.
I know what near-death is like......because I have died many times, and have come close to dying many more.....on Hardcore.
I play softcore....at game launch because Blizzard too scared to unlock Hardcore....on Hardcore.
I am hardcore....on Hardcore.