They might not be. If they give every story one clap, then their one clap is worth the same (to the algorithm) as fifty claps from someone who gives every story fifty. According to Medium, the algorithm measures clapping individually, by comparing claps given by each reader to how many claps they've given to other stories. I only learned this the other day, and it feels like the sort of stupid and costly complication Medium would do to measure 'quality' instead of dealing with actual problems.