The only logical reason for this in my mind, is this : The person must have made huge profits from Satoshi's technology... and he or she wants to show their appreciation to Satoshi for this. (Even though Satoshi has never used any of his coins and will most probably never spend the 4 bitcoins that was send to that address)
It is thus only a gesture to make a statement .....and not anything to do with the monetary value of those coins. (In a few years... those coins might rise to the Lazlo pizza level ....and people will make fun of this)
Whoever the person was and who knows what's behind the reason, he really did it in a way that was beyond anyone's expectations, no one thought he would think in that direction.