Unfortunately, the stupid losers at Microsoft and Apple never picked up on this, and eventually the glyph for the apostrophe was standardized as that ugly vertical piece of shit you probably see on your screen right now, which comes from the typewriter days when you would overstrike it with a period in order to make a shitty exclamation point, thus eliminating the need for one key on your cheap-shit typewriter; and the backtick was standardized as being an accent grave with no fucking letter underneath it, which makes a lot of sense when you're printing things out on a fucking dot-matrix printer with backspace, but not on a VT100, let alone a fucking window system.
Well, in the early 2000s, the folks at the X Consortium decided to standardize on making X-Windows apostrophes look like the shitty Microsoft Windows apostrophes, instead of waiting for the douchenozzles at Microsoft to catch up to the ASCII typography we had in the 1970s. So now instead of having shitty quotes only on Microsoft and Macintosh systems, we have shitty quotes everywhere, unless you use non-ASCII characters. (To be fair, all the glyphs looked shitty on X back then, so it's not like we were giving up some kind of Caslonian paradise.) The saving grace is that you actually can use non-ASCII characters now, and they will work everywhere with no problems. They look like this: âHello, world!â .
Anyway, the reason you still sometimes see the old kind of ASCII quote marks is that not every fucking document on the web gets thrown away in six months, because some of us fucking try to write shit that people will still want to read ten or twenty or a hundred years from now. When you see ``this'', you're looking back in time, to the days when characters were bytes and men were men. I mean, you’re looking back—oh, fuck it.
It's deliciously ironic that they do not display properly for me in your post (Chrome on Windows here).