Every host and agency offers "maintenance." For most, that means a monthly plugin-update run and a green uptime badge. Useful, but it's the floor, not the ceiling.
Real maintenance is about knowing the site well enough to catch problems before they surface: watching for slow queries after a plugin update, spotting a checkout regression before a customer does, and keeping a staging environment that mirrors production closely enough to trust.
The difference shows up in the relationships. Most of ours are measured in years, not projects. We maintain what we build, and we treat maintenance as engineering — not a subscription line item.