That's exactly wrong. They have the same processors as used in phones, which means they have hardware level decoding for video. My B+ can stream massive 1080p blu-ray rips over ethernet with zero problems. They make fantastic HTPCs.
My phone doesn't ever play 12GB blu-ray rips; and the rpi hardware is older than current phones (which use armv7 and armv8). Given the speed of the cpu, it's surprising it can decode a full H264 stream.
But It's good to know. The down-vote seems unnecessary.
