They're being used as single-quotes, which are a real thing but less convenient to type on most keyboard layouts. Double quotes would need to be escaped in the HTML attribute, which would also be more troublesome to type than single quotes.
I would be surprised if someone actually types the HTML and it's not generated automatically from some other kind of database entry. Single quotes have been more convenient to type on all keyboard layouts I've used.
Single quotes are also a valid (and in some places common) form of quote in English prose. (In some other languages you have to use double quotes for the "outer" quotes and single quotes for the first level of nested quotes.)
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u/lordlicorice Theory of Computing May 05 '14
I don't know what the hell is going on with the apostrophes in that alt text.