Based on if they made healing req higher:
They would go OOM, and such healing would be too weak ^^
DPS and Tanks have expectations to their role..
so why shouldn't healers too? other then just do good dps?
Increased healing requirements does not make healing itself harder!.
it just means you have to press your heal buttons more often ,
rather then pressing your 1,1,1,1 dps button..
Also healing requirements should inc gradually with your level....
that way even new player can learn..