Honestly, the point of 'crediting icons so that people will know where to get them' has gotten a little moot by now. There's the memories of pb_updates and wikicon to check if you're at a complete loss. But even then, most iconmakers here on IJ have a very distinct style that you learn to recognize after a while. I could recognize blevcons', robins', oslo', seethesoldiers' and rpg_icons_ita's (and so many others) icons from afar.
That's just icons, though.
With HTML, it's harder, of course. There's no distinct style you can put in your coding, other than putting a stamp on it, which can easily be removed. That's why this community is such a blessing, for those that know about it.
But I'll agree with what everyone's said, crediting is still common courtesy.