It works per user because update checking is done from Max, which runs in user mode. If not, Update Manager would require admin rights each time it runs, which is a worse approach.
We have plans to include an 'admin' mode for Update Manager, for customers that prefer that option.
Until then, please see this FAQ
entry. It describes how to configure RailClone and Update Manager to use a shared network path. Basically it's the same process we want to include, but configuring it manually.
I hope that helps.