I work in IT, and different definitions of what SaaS means are starting to wreak real havoc on the architecture as a whole.
We are better served just quitting the acronyms and taking the time to talk about a more detailed description of what the service actually adds in terms of value.
Amazon Prime is a subscription for shipping, video streaming, gaming benefits and more. Since software is not the primary goal, but a means of delivery for these other services, I will not consider Amazon Prime SaaS.
Slugs to be you then, I guess. :P
In all seriousness, the graph shows different species as fraction of total uses recorded. Since the paper is mostly about mice, and behavioural differences under different circumstances, it being unfair to the slugs is probably not such a big deal here.