Just about every trendy hipster person I know has read Eats, Shoots and Leaves and enjoys The Oatmeal's explanations on grammar as well. My guess is that it fits into a few key trendy hipster values:
1. A chance to feel better / look down upon others. This is especially true with grammar geeks (like myself, who is sort-of Trendy Hipster Light) who were frowned upon by peers during their childhood.
2. A chance to engage in an art that is vastly becoming irrelevant. Like learning shorthand, speaking Old Norse or having a typewriter on hand, learning grammar lets trendy hipsters engage in a geeky endeavor that lacks any real practical element.
3. A chance to be ironic, or when that fails (often) a chance to find unintended humor. Once you master grammar, you can mock the subtle irony found in signs, in books and in music. So, I can laugh aloud when the football announcer mentions that "Philadelphia literally has an explosive offense" or "The Giants literally destroyed the Cowboys." Nope, despite my initial hopes, the Cowboys are still a football team.
I have a hunch that trendy hipsters will not procreate as much as other segments of the population. Which is too bad, honestly, in terms of language lovers. However, in the long run, they might just be the very subgroup that keeps grammar intact.