Simple fact from a programmers prospective. If funcom uses the system I assume they do, then implementing the 50% damage was simple, they just did:
if(target=="player") dmg_output()/50
Now that works fine because they have the "player" tag defined as another player object. The problem with 50% heals is, ruh oh, they can't just enter if target is player do 50% heal... the target is ALWAYS player, hense nerfing all heals PvM and PvP. And being someone who is working on another mmorpg project for a company let me tell you, if the engine is much like the ones i've seen then making a zone specific healing system would be an ENORMOUS hassle. Not to mention if they say in 25% or 0% zones only is healing halved, what about all the places you huntin 25%? or what about PW and DAV? Sorry the code doesn't click. And from what I understand you can't have a variable change so that if you are in combat it will instantly change the potency of your heals then change back to 100% as soon as you exit combat.
Changing the heal system is near impossible from a programming perspective, I have just realized this and asking funcom to change it (which they never would im glad) would probably result in a 6 month delay before our next patch, or longer :/
So please lets sotp discussing it altogether. Ask for 100% back if you wish, but healing will NEVER be changed, trust me.