Off topic:
Yes my avatar is simca from air gear,
but my sig is yoko gurren lagann
on topic:
I dont know why they honestly thought that they needed to do this. Runescape was perfectly fine without the 10x health and damage. But i guess thats just me.
Well as an MMORPG, they might've wanted to be like other MMORPG's and do high dmg/have lots of hp.
Most RPG's, you go into the thousands and maybe even ten thousands when at max hp, so RS probably felt left out with their double digit health points.