Well, you're not going to see a mass produced toy that has sanded parts. Short of using a water knife or someone switching out or sharpening the cutting surfaces every half dozen cuts, you'll never have a mechanical system sharp enough to minimize sprue marks in the way you're suggesting.
And just for kicks, I looked at my takara transformers, MP, binaltechs and alternity and they all have sprue marks. Several of the binaltechs have rather hideous gouges from where the sprue was obviously snapped off instead of cut off.