This post sort of makes a good point but also somewhat insinuates that you can spend a week on something like D3.js or design and then call yourself, "X" it is good to learn new things and never confine ourselves to what skills we think we should know, but I feel it's somewhat of a smack in the face to others who spend hours, days, weeks, months and years perfect their craft only to find themselves working with others who feel as though they're entitled to call themselves the same. Just because you learn the basics of something doesn't make you an expert nor give you the right to a title of said skill. I know the basics of car maintenance and repair, does that give me the right to put, "Developer and Car Mechanic" in the title of my website or resume just because I hustled the knowledge of basic engine maintenance and repair?
Is Johnny who's been designing websites for 2 weeks now truly able to call himself a designer when Michael who's been designing websites for 12 years is also a designer? It doesn't feel fair that anyone can label themselves based on only little amounts of experience. I guess "Johnny - Developer and Junior Designer" doesn't have the same ring to it, "Johnny - Developer and Designer" has.
You might be able to learn how to increment a counter, set a timer and master if statements and functions in Javascript in about a week, but you'll never truly learn anything in a week, you're just scratching the surface you don't know about all of the methods the String object has, you don't know about closures, global variables, xmlHttpRequests, prototypes and dealing with arrays. There's a difference between learning something and actually learning something well. Sort of like those, "Build a blog in 20 minutes" tutorials most languages love to perpetuate when describing how easy their language or framework is.
As for the statement that developers can design, I disagree. It has always bugged me when I see a business advertising for a designer and developer, you can't truly do both at once and do them well, it's merely a way for businesses to skimp on hiring two great people instead of one mediocre at best (if you specialise in $200 websites then maybe it's fine). In my opinion you're either a designer or you're a developer. I'm a developer and I've been trying to design my own sites for my ambitious personal ideas for about 3 years now, but I lack the knowledge of grids, colours, typography, ideal reading lengths, line heights and all of the other advanced aspects a designer faces. If I were to call myself a designer, I would feel like I'm insulting the actual designers that I work with and respect. Most of the designers I work with know a little CSS and HTML but they don't call themselves developers because they know that knowing the basics of something isn't enough to be good or even mediocre at it.
Would you trust a car mechanic who decides he's going to give hairdressing a go? We all use different parts of our brains, we have our own likes and interests and these are what make us great at what we decide to do. People become mechanics because they have an interest in engines and getting their hands dirty, they have a thirst for mechanical knowledge just like developers are mostly people who grew up taking things apart just to see how they worked, endlessly reading other peoples code and the desire to solve complex issues with a text editor and a keyboard.
I'm all for learning new things, but pretending to be something you're not is something I do not advocate. Now if you'll excuse me, I've got an oil change and haircut appointment to attend to...