Technology of optical drive as dvd blu ray r pretty old now. Incompatibility arises with new technology. Say a particular feature created by some manufacturer. their feature may not work till u install their updates.
Like wise is the case of hard disk. Newer and bigger hard-disk may be not detected by ur os/motherboard correctly. There also the manufacturers provide some form of work around or update.
As regard to computer case, all makers follows a standard size dimension guide-lines. So everything from case, optical drive size etc have standard size. etc etc