They probably put the tank in the bow for weight and balance considerations.
This would reduce the weight in the stern and/or free up the engine compartment for some other peice of gear they were trying to squeeze in.
It would also allow them to keep a variable weight on the centerline of the boat.
As to the wisdom of this decision.....
My 2006 260DA is docked right beside an identical 2005 260DA and it is amazing how much lower his bow sits in the water compared to mine. Conversely his aft section sits a lot higher than mine at the transom with an additional (estimated) 2-3 inches less of the hull in the water. All of this is undoubtedly due to the weight of his water tank in the bow. I think Sea Ray moved the tank in 2006 primarily because the fill location wasn't too convenient on the bow (2005 model) compared to mine which is on the starboard side just under the spoiler. Obviously another plus is if mine leaks it won't flood the cabin. It also gives you a way to balance the boat side to side (which becomes an issue when the holding tank gets full) because the water tank is on one side of the boat and the holding tank is on the other.