Never seen ref spam not get deleted, do you have an example of this?
Such situations are very rare. I'd say that 99.9% of referral links get deleted. Those that have not been deleted have most likely not been seen by moderators. However, sometimes when we're talking about something extremely constructive, then a referral link might be allowed.
What SebastianJu describes does not sound constructive to me, thats why I was wondering whether it actually happens that often or they just feel like it does.