In the title of the post I saw currently on your page (31 May 2011), the single quotation marks are displaying correctly in the header, and are correct, as well in the final quotation of that post, but then I see that you have others in that same post that are displaying that strange behavior.
Are you using Word and cutting and pasting? Because when I cut and pasted your text into my visual editor, the problem remained. It looked "normal" in html mode only because there are no "smart quotes" in the html mode, and only by previewing it or switching to the visual editor can you see whether it's a smart quote (inverted commas) or the plain-text sort of straight up-and-down mark. I ask because I was able to eliminate the problem both in the Coraline theme and in Quentin quite simply. Cutting and pasting from Word (or similar program) can sometimes cause formatting problems.
I successfully corrected the problem by deleting each of the single quotation marks (i.e., inverted commas) and retyping them. Voila! When previewed, they appeared to curve in the correct way.
I've noticed sometimes with some fonts on one of my blogs, if there is a character with an accent mark over it, a closing quotation mark doesn't appear properly, but I "solve" that by using the "insert symbol" feature. So if simply going back and editing them in visual editor doesn't work for you, you could do that, although it's a pain.
I hope that some of this may have been helpful!