Depends what we're talking about. As Spunkey says, most people just charge a single rate for their time as a 'web developer', otherwise it just gets too complex and pointless.
However, if we're talking about the roles of front-end web developer vs back-end programmer in a proper professional environment, then yes, they should be charged at different rates. They are two very different disciplines and require different skills and personalities.
Markup/CSS is, in essence, just about formatting and structuring a document. It doesn't require much logical thinking. If someone has the ability to format a document in a word-processor, they can pretty easily grasp the concepts behind HTML. That's
certainly not to say it's easy; many people have the ability to write HTML/CSS, but
few can actually write it well. Producing good markup and CSS is an artform, and drag'n'drop in DW certainly doesn't figure in that. Front-end web developers aren't 'cheap', good ones do (and should) demand a high-rate for their skills.
PHP, on the other hand, is a programming/scripting language and requires a whole different set of thought processes to writing markup - mathematics, logic, problem-solving and so on. Good programmers are often (but not always) products of computer science degrees and as such, demand a greater rate. And same again, many people can program, but few can program well.
an hour of your time is an hour of your time
It is, but not when it comes to work. You should get paid relative to the effort/skill involved. An hour of your skills is an hour of your skills, I would say is more accurate. Should a specialist doctor be paid the same as a burger-flipper?
As for quibbling semantics, no I don't class HTML as 'code' either, it's just a descriptive language. Code is about providing instructions to
do something, while HTML/markup is simply
describing something.
I'm sure someone will come up with a better distinction.
Do they cross over? If I'm developing a site with PHP, it never mixes with HTML/CSS. That's left to the template/front-end developer (though that's actually typically me too

), who only needs to know HTML/CSS. If I was freelancing on a job that was solely programming/scripting, I personally would charge a higher rate than if I was writing HTML/CSS. However I wouldn't charge more for CSS - just the same as HTML.
If I had a rate card to tender for work, I would put my hourly rate in order of price as follows:
- HTML+CSS
- HTML+CSS+JS
- 1/2 + PHP
- 1/2 + PHP + MySQL
And, funnily enough, if you go looking for contract work, that's the relative rate differences you'll see.