Wow. This is the first time I've seen them all next to one another. That's crazy. I knew the One was bigger than the PS4 but I had no idea it was bigger than the old, bulky PS3 too. I guess I imagined it was roughly the size of the 360. While that's kind of true, I'm shocked it's actually larger. Given the advances in technology I assumed we'd be going smaller, not bigger.
I'm also shocked by how small the PS4 actually is. Again, I knew it was smaller than the One but this is a pretty significant difference.