beads and gem jewellery

I'm obviously no expert, so I'll ask what's probably a stupid question. I've
seen prices of gemstone beads. Why are they so inexpensive compared to
gemstones used for jewellery? I heard that gemstones used for beads are
always those whose optical characteristics are not good enough for use in
jewellery. That's why they're mostly cabochone or sphere shape. Is that
true? Does that mean that beads can never be as clear, and as rich in color
like those gems set in silver or gold for jewellery?