mullenweg, founder of wordpress, claims that the apostrophe we type is actually a prime mark and talks about how he always manually inputs U+2019 instead

He’s right, though. They’re different characters, and they look different. The curved apostrophe looks much better, especially with larger fonts. I don’t use it in casual typing, but it’s important for official copy on the Web. You can use Option-Shift-] to type it without the alt code on a Mac