On the other hand, what are the differences of the two industries?
In some aspects, there are similarities between the two professions. I might be old fashioned, but I believe these two roles are very much separate roles with different responsibilities, but the same end game. I am seeing some parts of web design converge on more code-driven design in the form of prototyping using HTML/CSS.
Which is great for me, because it means the days of cutting out assets and reading animations/transitions off a spec document are sunsetting behind us. As we move toward designing in code and not just in Photoshop, I believe we will start to see even more overlap.
A lot of web designers these days know some form of code, at least the ones I have worked with. I wouldn't call them front-end developers though, knowing a little HTML and CSS does not make you a developer. I know a little bit about design, but I wouldn't call myself a designer either. I think attention to the finer details is a skill that both professions share, although, the most pedantic designer will notice details that most front-end developers will not.
I know how to knock up a basic web layout, but I really lack the core fundamental understanding of grids, golden ratios, typography, colour theory and other more deeper aspects of design that tinkers don't get exposed to. Just like designers who code probably use jQuery instead of natively supported browser API's and methods that can do the same things more performantly.
Can you be both and be great? I am sure there are some freaks out there who are, but they are pretty rare. You can either choose to be a specialist in your chosen field of design or development, or you can know a bit of both and know just enough to get by to be considered good, not great, but good.
Remember the saying: Jack of all trades, master of none.