My intention was not to say it was a "Windows Thing"...just that there may be reasons the OP is writing zeros to the hard drive which may have good rational due to their previous 10+ years of Windows computer experience.
What I'm saying is...writing zeros to a Macintosh hard drive before installing the OS is just not necessary...that's what my 23 years as a Macintosh user has taught me!
As far as the "zeros" you're writing to the hard drive when you sell a computer...of course I agree with this practice! You're writing zeros to your hard drive for a totally different reason than what the OP is talking about!
You're writing zeros to the computer's hard drive you're selling totally for security reasons (secure erase). The OP is writing zeros to a hard drive BEFORE installing the OS on a new computer...which I'm saying is not necessary.
- Nick