It's the same exact software... except as Jim noted... there are a few "extra" things that only work in IPS' custom setup:
Available now...
Real-time Who's Viewing/Who's Typing
Trending module
AI image tagging/moderation
Coming soon...
Live Topics (live chat during a webinar allowing interaction with members during live events that later are turned into forum topic)
Video encoding (transform videos into one format that can be played across all different platforms/devices)
I agree in that the biggest value comes from not having to deal with all of the underlying plumbing. No worries about installing the software, or making sure you have compatible modules, or finger pointing between host and IPS, etc. Instead of worrying about how to "stitch it all together" between your hosting company and IPS... worrying about things like backup, security, etc... you're giving the full headache to IPS to worry about.
This is great for some people to have a solution like Gmail where they just use the software. For others, they prefer to get their hands dirty and control every step in the stack. In those cases, the self-hosted version is a better solution for them.