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The intent is to use the material in orbit. It costs loads of money to send stuff to orbit (e.g. for the ISS) and this could be cheaper, especially for bulky stuff.

Bringing it all the way back to the surface is not worth the energy required.

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The intent is to use the water in orbit, but they're saying they'll bring the platinum down here. If you're already in earth orbit, going back to the surface doesn't take much energy.

If we want to move stuff around in space what matters is the delta v or change in velocity. Fortunately since we are de orbiting a satellite, we can use aerobraking http://en.wikipedia.org/wiki/Aerobraking. So we just need to slow down the craft and a make fall with a parachute. If we had to lift the mass off the moon or mars we would have to spend a lot of money. Just getting it to the surface of the earth from orbit is much much cheaper.

But don't you need to spend a lot of money to prepare the material for reentry without losing most of it?

No. You only need to use special technology if you have to limit the g-forces for humans.

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