Re: @Andrew Orlowski:
It's not so much the amount of CPU use, but the fact it interrupts the CPU when it is trying to do other more important things.
For realtime work such as audio and video where you try to have as little latency as possible (pressing a key on a keyboard or moving a video controller) this can be a deal breaker. Less CPU interupption and more stable timing means you can drop the buffer sizes down.
DMA isn't anything new, an Amiga 1000 from 1985 had it. So gawd knows why the PC compatible world likes cheap shitty non-DMA hardware. You wouldn't go back to PIO mode hard disks, the performance leap when UDMA came out was amazing. So why settle for USB.