This is a problem even if you don't buy pre-built. You're going to be buying similarly specced drives at similar times and you're probably buying from vendors from the same rough geographical area so chances are you're buying drives from the same batch anyway.
It used to be worse: all the drives in a RAID setup had to have the exact same specifications or the thing wouldn't work, which pretty much guaranteed near simultaneous failure of multiple drives, but even today, with somewhat more flexible software raid setups, it's still a problem.
At a place I used to work we used to joke that a drive failure warning from a RAID controller was nothing more than a signal to get out the backup tapes and start building a new server.
It used to be worse: all the drives in a RAID setup had to have the exact same specifications or the thing wouldn't work, which pretty much guaranteed near simultaneous failure of multiple drives, but even today, with somewhat more flexible software raid setups, it's still a problem.
At a place I used to work we used to joke that a drive failure warning from a RAID controller was nothing more than a signal to get out the backup tapes and start building a new server.