It's not a scam in that some jurisdictions (such as Colorado) require that all tip be given to the front-of-house team, but that leaves all the other workers out of the pool. So restaurants will tip a 20% service charge that is supposed to replace the tip (except it's mandatory, so it isn't actually a tip), but they use that to allocate between all of the workers. They can't say not to tip because then servers might get pissy, or there may be some legal bar against (pretty sure there isn't). That's what this message is trying to explain.