Yes. It used to be that the bottle caps were of a different type of plastic and so couldn't be recycled together, at least not easily. And people learnt that, so they used to remove the bottle caps.

But they've gone over to using the same type of plastic in the caps as they do in the bottles, so they can all be recycled together, but getting that new idea through to people is a bit difficult, so it's easier to just tie the bottle cap to the bottle to reinforce the idea that they should now stay together.