This may be confirmation bias, but it feels like this guideline is more honoured in the breach than the observance.
If you actually followed the guideline, you'd likely be waiting a while for the service to be added, and you may not notice it when it does get added.
If you make a metatalk post asking for it to be added: e.g. (1), (2), there's a non-zero chance that pb will add it immediately, and everyone gets to have a nice chat about the service, its merits, and what our account names are.
Given the incentives to ignore the rule, is it still a sensible one?