You can get any frames.
I debated saving the money on the frames and just using my old (15 years!) frames. In the end, I sprung for the new frames and I was pleasantly surprised that I did.
The new ones have a middle bar that runs lengthwise down the middle of the bed, which would seem to extend the life of the box springs and mattress by reducing their ability to sag. They are also expandable to any size bed in the future, from twin to king.
If you already have a frame like this, though, or you can get it cheaper elsewhere, yeah - no need for new ones.