This makes sense. I'm pretty sure that tests that I've run in the past using bonnie++ or iozone showed faster reads with raid1 than with a single drive. I would think that if the drives are on seperate controllers (and depending upon the performance/capacity of the drives and controllers), there could be notable improvements.
with SATA or SAS, of course, every drive is on its own channel. even with PATA, at 100 or 133Mbyte/sec, only the fastest newer drives would saturate the bus doing two transfers concurrently.
now, after i wrote what I did above, I dug up the kernel.org 2.6.18 kernel that RHEL/CentOS 5 is based on, and it still had the older code sequence as shown in that 'to do' list entry... but I didn't run the RHEL patch sequences against it, its quite possible RHEL retrofitted this patch to it.