When I started out as a PO I did that myself as I haven't yet realized the consequences. Today, I totally agree with you and am sometimes a little bit stunned if I even see a rather experienced PO practice this (Don't ask for an example now, I don't recall specifically, I only recall noticing).
What I also used to do way back is creating "accounts" for tracking purposes. For example if I was going to advertise on XYZ I would create an account with that ID. If I got referrals to that account, spread them amongst my upgraded members.
What also is not a good practice is having one's admin account set to for example 500 ref-rotation. Having it set to 1 maybe 2 to give those referrals away in contest etc. is perfectly fine with me - but not ridiculously stealing from upgraded members.
JM2C
Claudi
ETA for typos