then you are running an old version of WordPressMU as it was renamed multisite and incorporated into WordPress itself several versions back. MU itself is no longer supported.
Also there's nothing to stop you from continuing to use VPS or whatever. Obviously you would use one WordPress install per hosting account.
Provided it is set up the right way you could still move individual blogs between hosting accounts as needed.
So the only time you'd have 10 WordPress installs that all need updating is if you have ten separate hosting accounts full of WordPress blogs.