Your dealership provided you with poor service. No doubt about that. Once you told them that you had to keep giving your battery a jump, they should've replaced your battery under warranty (battery is covered for four years). Once you jump a battery and drive around for a bit, the battery can test just fine. The issue is, can the battery hold a charge and that's something that can't be tested unless they hold your car overnight.
I had the same exact problem as you did back in November of 2010 on my 2008 RX350. It had about 42,000 miles (about three years). I had to jump it every time I wanted to drive it. When I took it to the dealership and explained the problem, they gave me a new battery under warranty quick and easy.
I've also googled this problem and it isn't as uncommon as you would hope. Other owners' batteries have also died at around the three year mark.
