Is this a similar "sync" like thing going on?
Yes. DiskSafe first forcibly (sp?) closes all files, sends an ACTION_FLUSH to the file system, then waits for the file system to shut down motors (as a work-around against FFS versions < 44 ACTION_FLUSH not being synchronized as it should), then inhibits all file systems listed.
Ideally, this should really be part of a file system function (ACTION_SHUTDOWN or something like it), but it isn't.
And if yes, would it not be neat with a C:reboot that would do the same? 
If the reboot goes through exec/ColdReboot(), then this is exactly what it does. ColdReboot() is patched to a small function which signals DiskSafe to take over and shut down the machine instead.
If, however, C:Reboot simply runs into a RESET instruction, then there is nothing I can do. It probably won't work in first place on a couple of machines anyhow. The reset instruction resets the external hardware, but not the CPU.