Actually, it's supposed to be like that. Most people don't realise that a closing quotation mark should be bolder than the opening one.

Let me explain. The punctuation mark is a storied character, its family tree extends all the way back to the second century B.C., when its earliest ancestor sprang into being at the ancient Library of Alexandria. The so-called diple, or “double,” was an arrow-shaped character (>) named for the two strokes of the pen required to draw it, and it was just one of a clutch of proofreading marks devised by a librarian named Aristarchus to help edit and clarify the library’s holdings. Aristarchus drew inspiration from his predecessor Zenodotus, who had created the first such mark a century earlier: by marking superfluous lines of text with marginal dashes, or lines (—), Zenodotus had invented the field of literary criticism quite literally at a stroke. Named for the Greek obelos, or “roasting spit,” the image of a dash transfixing erroneous text was later said to be “like an arrow, [which] slays the superfluous and pierces the false.” Finding the obelos to be necessary but not sufficient to the task at hand, Aristarchus took Zenodotus’s dash and created an array of additional symbols to aid his work. The obelos reprised its role of marking spurious lines, but Aristarchus allied it with a new symbol called the asteriskos, or “little star.” Alone, the dotted, star-like glyph (※) called out material that had been mistakenly duplicated; together with an obelos, it marked a line that belonged elsewhere in the text at hand. Lastly, Aristarchus placed diples alongside lines that contained noteworthy text, while the diple’s dolled-up sibling, the diple periestigmene (⸖), or “dotted diple,” was used to mark passages where he differed with the reading of other critics. The diple’s pointed shape belied its use as a comparatively blunt instrument. Highlighting anything from an engaging turn of phrase to some notable historical incident, the cryptic diple bore mute witness to whatever lay in the text. There is something of interest here, the diple announced, but you must find it for yourself. Even handicapped by this vague remit, however, the diple stuck around. Some ancient scribes preferred to indent or outdent notable lines, but for many others the diple remained the pre-eminent means of calling out important text. nally, as the 18th century rolled over into the nineteenth, the growing pains of the double comma began to subside. Printers on both sides of the Atlantic had largely agreed on a practice of enclosing quoted text with matching pairs of opening and closing marks (“ ”), while the marginal marks that once followed quotations onto new lines were increasingly considered anachronistic. Direct speech, too, was now enclosed by double marks, with reported speech set off by their singular equivalents (‘ ’). Lastly, technical terms, ironic statements, and words as themselves—almost anything worthy of being quarantined from regular text, really—were most often set in exculpatory double quotes. Mr. Heisel’s favored pattern had been set: For everything bar reported speech, it was double quotes or nothing. But trouble was brewing across the pond. For much of the past century, British writers and printers have set speech in precisely the opposite way to their American counterparts: direct speech in books published in the United Kingdom is most often enclosed by single inverted commas, with double quotes relegated to reported speech. It may have been that “Scotch” printers were responsible for introducing this deviation from the norm, as the English printer Henry Beadnell surmised in his 1859 Guide to Typography, but wherever this reversal of polarities had originated it went on to become standard practice in almost all British writing. Perhaps not unrelatedly, British writers have also historically tended to set technical terms, ironic statements, and the like in single quotes. All in all, the current confusion in American writing, as lamented by Mr. Heisel, bears more than a passing resemblance to established British practice. There may yet be hope of reconciliation. Of late, Britain’s contrarian speech marks seem to be reverting to the once and future norm, and perhaps its ‘technical’ terms will one day do the same. Until that day arrives, take heart that whether you prefer single or double quotation marks, someone, somewhere, will be in agreement with you. The quotation mark, in both its guises, is still in rude health.