Do people really like that sort of thing [big butt plugs or nipple clamps, say]?

Yes. People like a great many things, and we attempt to cater to as wide a spectrum of desires as we can. Desire and pleasure are very individual things, meaning that what's statistically average or considered "normal" isn't necessarily what revs your engine. Lots of stuff is especially fun precisely because it's taboo or uncommon. All this erotic diversity means that everyone is different, not that any kind of desire is better or worse than any other, regardless of how mainstream or exotic it may be.