Why do you do this ?
Is it impossible to get it to work otherwise ?
(adb remount is not exactly difficult to do)
Its convenient because you can test a command knowing it will fail and then remount it if you need to.
I can only guess at how much more hassle for people trying to use a touchscreen for file management have.
(If there is something to do with breaking recovery etc then that is a valid reason).
There are benefits to a minimal amount of changes.
it makes things easy for all users... if u want more control over things & if u want to lock system in RO mode just save the following as a file in /system/etc/init.d/
#!/sbin/sh /sbin/busybox mount -o remount,ro /system