I'm a programmer working in web "development", and some of the things you lay claim to (UX, UI) are things that I'm responsible for rather than our "designer".
So I guess there's really a spectrum of different types of activity (rather than a binary partition) and the choice of who gets what responsibility is a local one.
Some organisations have people who have exotic job titles with words such as "User Experience" and "Information Architecture" in them. I suspect that "designers" and "developers" in those organisations have much more clearly separated roles.
I dont' really see them fundamentally as different. I was just pointing out stuff I was also doing which could might as well have been done by a developer (in fact I worked with a couple developers on setting up the proper architecture)
The "pretty" parts is such a small part of what design is all about.
I don't just create some skin on top of some application, I help create the underlying structure maybe even the business logic.
Also developers are not just making the things work. They are actually constructing the code space by making decisions that are based on some aesthetic principles. When you construct your code in a certain way it's not just rational it is as much emotional.
To give you an example of what design also is.
We recently managed to convince a bank to put some of the knowledge they had about their clients into play. Basically all transaction come with a unique vendor number that can be paired up to a category (utilities, groceries, insurance etc) and allow customers without having to type in a single thing to see how they spend their money.
The original design I did was nice and cool and all, the final design ended up looking rather pale in comparison, but it's one of the things I have done in my life that I am most proud off.
It took not only knowledge about how some of the innnerworkings of banking, it took political fights, fights with IT departments and so on.
But the results where phenomenal. People loved it and I neither they cared that it wasn't as sassy as I had originally intended.
Design is not just about how it looks, it's as much about how it works.