Difficulty has no bearing on endgame or hardcore content. Hardcore content is a measure of time investment and punitive systems. GW1 has a great [punishing] DP but you will never have to grind up gear, rep or invest weeks into clearing missions.
All the Guild Wars games are casual as in drop-in/drop-out focused w/ little to no barriers to entry aside from player ability. Player ability having no bearing on design. Until recently in GW2's fractals, natch.
[Re-rolled a Mesmer to do Winds of Change. Love GW1. I think it one of the finest games ever made. Far superior to the sequel. ^___^]