Description:
Actually a vanilla 'grub-mkconfig -o /boot/grub/grub.cfg' fill all whit the common stuf exept that add a ro in the command line
this make mkinitcpio (whit the fsck hook added as is recommended [actually])
complayn at boot for a filesystem mounted as ro
one can fix this manually but subsecuents grub-mkconfig-ings going to override that

this problem as far I know is:
line 138 of /util/grub.d/10_linux.in

linux ${rel_dirname}/${basename} root=${linux_root_device_thisversion} ro ${args}

A simple seed that change it to rw (or remove it and translating to /etc/defaults for give control to the user of that option and aboid break configs) can by a solution

Additional info:
* grub 2.00.5xxx

Steps to reproduce:
make a grub-mkconfig and rebuild the kernel with mkinitcpio 0.15.0
and reboot, watching a molestously message in every boot