Same topic has been discussed before
And i think this restart is required because in most cases rpm apps use same dependency or same package for system also so updating a app could change that part of dependency which maybe required to run the os so it is safe to restart maybe that was the reason why gnome and fedora team implemented this in that way. But in some case i also thought that it is maybe over reacting for a restart so you can put a post in bugzila about this issue because most distros don’t ask for restart.