Right. In the shower, I also realized that this is just comparing averages- if, say, 10% of the population really hates spoilers, but the other 90% enjoys them enough to make the average for spoiling higher, it's still sensible to put spoiler warnings as a courtesy to the 10%, because the comparison is "cost to warn vs. benefit of warning" not "spoil for everyone or spoil for no one."
It's worth noting that the experimental setup involved putting spoilers into the opening of an unfamiliar story - that is, the subjects didn't know they were being spoiled. Suggests that if people enjoy stories less after learning spoilers, it may be their own fault (akin to all the studies on wine and perception).
The latest SMBC made me laugh a bit, so I thought I'd bring extra LessWrong attention to it.
I don't know if pointing out the subject of the comic in advance will make it more or less funny. Knowing that might be more data regarding that recent study claiming that spoilers don't actually spoil stuff...