i beleive a few boxes got banned do to a drive upgrade during repairs, where the drive was originally a Ms25 and got banned for having a Ms28 after a repair. all the banned xboxs from that got un banned. thats if i remember it all correctly.com.
its not a reliable method because newer drives cannot be read without disabling the firmgaurd, so that cuts down the amount of drives being read. and with the ixtreme ms25 firmware being based on ms28 firmware which has firmgaurd, that reduces it even more. with hitachi drives requiring mode b to read the firmware, that pretty much rules out any modded drive being read over xbox live (unless you still have early Xtreme firmware based on the Ms25)
so who can they catch if they can only read non-modified Ms25's?
with new xbox's, as you say record the drive type, will all have an updated and newer drive, therefor have firmgaurd.