In parallel, major slave revolts in continental North America also happened about once every generation (it's hard to compare to peasant revolts because the historical record is better).

For a striking contrast with North American slavery, consider the case of slavery in ancient Greece and Rome, where they where, despite the occasional rebellion, sufficiently confident in how much control they had over their slaves to use them as cops and prison guards.

What exactly is the difference?

I'm falsifying John's claim that most inter-factional conflict focusing on issues of inequality is a historical universal.

Giving the peasants what they wanted would have reduced inequality. I assume the peasants leaders were smart enough to notice that fact.

That fact only seems as salient as it does because we live in a culture that places high value on equality. For another perspective look at how Confucianism is able to combine a justification for peasant revolts under some circumstances with support for a strong social hierarchy.

Surely that isn't evidence that the slave population didn't express (or desire to express) complaints about inequality when they weren't engaged in armed uprisings.

The difference is that the slaves lived in a culture where "all men are created equal" was already an established meme.