Why doesn't Ubuntu require restarts on more updates? I know that for kernel updates and things like video drivers, it can't load the changes without a restart. But I'm curious about more basic updates of pretty fundamental packages that often don't require restarts. Things like Telepathy, glibc, gtk, etc. Why don't packages like this require a restart to be updated? Is the new version actually running right after an update?
Another example would be Gwibber. I recently received and update to gwibber via the Update Manager while gwibber was running. The update completed successfully. Would gwibber be running the new version without manually restarting it? And is that the same for other packages? (I know some like mysql and apache automatically restart on an update). For packages that don't automatically restart, can't that be somewhat of a security issue for security fix?
This comes up because I have been running OS X for about a week and almost every update requires a restart even if it isn't kernel/video driver related (as far as I can tell - they don't give you a lot of information). A friend of mine said that Apple forces restarts on most updates "just in case" it would be weird if you didn't restart. Windows is the worst because almost any install/uninstall or update requires a restart (often forcing shutdowns to take a very long time). This may be a bit broad for this venue, but why do the different operating systems handle this so differently? Or, more specific to Ubuntu: why doesn't Ubuntu follow a more strict restart policy?