Yeah - this is a bit of a sweeping statement really because even if *most* drives were active low, that statement takes no account of the fact that your BOB (for example) *may* be inverting the signals before they even get to the drives.
The way to do this correctly of course is to simply follow what the manuals for your various hardware say.
However if your machine is running OK I wouldn't worry about it. You can always try swapping it and see if you notice any difference in the performance of your machine.