It's only confusing when the paladin tries to use Lay on Hands on themself. Look at what happens when they cast it on somone else and the reason becomes clearer.
Without that wording, you would have the power healing both the paladin and their target:
Step 1: The paladin spends a healing surge, and thus recovers hit points.
Step 2: The target of Lay on Hands recovers hit points as if they had spent a healing surge.
Apparently that's not what was intended, so they had to mention that the healing surge only fueled the power - it didn't also heal the caster.
Is the current wording perfect? Far from it! But at least we don't have someone arguing "So I use Lay on Hands on myself - and get two healing surges for the price of one!"
Without that wording, you would have the power healing both the paladin and their target:
Step 1: The paladin spends a healing surge, and thus recovers hit points.
Step 2: The target of Lay on Hands recovers hit points as if they had spent a healing surge.
Apparently that's not what was intended, so they had to mention that the healing surge only fueled the power - it didn't also heal the caster.
Is the current wording perfect? Far from it! But at least we don't have someone arguing "So I use Lay on Hands on myself - and get two healing surges for the price of one!"
