in Hacking

FreeBSD, (SuSE) Linux date differences

I wanted to retrieve yesterdays date with a format of YYYYMM
This was solved in FreeBSD like this:

date -v-1d  "+%Y%m"

(SuSE) Linux doesn't know the -v option
The same thing in Linux could be done like this:

date -d yesterday "+%Y%m"

Why the difference?