"Slavery in base game RimWorld is limited only to selling prisoners for profit, with no other use. The Ideology DLC significantly expands on the concept, allowing prisoners to be enslaved and forced to work and perform tasks."
For sure incorrect. I only have the Royalty DLC, and I can definitely both buy and sell slaves. Not sure if this came with Royalty or if it's in the base game, but you for sure don't need Ideology to buy slaves.
Buying a slave without ideoligion just turns them into a colonist, so they dont stay a slave, and there are no slavery related moodlets associated with it unlike selling, so I sort of understand where that wording came from, but you're right that its unclear/inaccurate. Please feel free to try to make it clearer.
Also this is your talk page, generally this should be on the talk page of the page in question. It's not a problem, but just for future reference.