I disagree. I don't find either bottle hard to get ketchup out of. But the big difference is what happens when you're done getting the ketchup out. With a glass bottle, I'm left with a plain glass bottle (and metal screw cap) that I can recycle anywhere, or use for just about anything. With the plastic bottle, I'm left with a weird plastic bottle that's really only designed for dispensing one thing.

Reusability is a big part of usability. Generic glass bottles excel at this.