I think the point is that rechargeable batteries don't last forever. I've already had to replace both of mine in my 360 controllers. Luckily, I got a pair of them for about $12. If I'd had to buy 2 new controllers, it would've been closer to $100.
Bought me ps3 one month after release (almost three years ago I think) and although I've bought the new DS3, the battery in my original controller wtill holds a long charge