To me it all seems to be very related to Audi's split with S and RS models. As we know Audi is much stronger in Europe and around the world than it is here in US, even though we see the incline of the brand in last decade.
In a sense M had been compared to S model for a long time in the past and where RS models were more extreme. Comparing performance wise RS to M could be done but as we all know RS was much more expensive than M and the production was much lower for the RS cars. In the whole practical and financial sense M was compared to S.
Now, we know recently that has changed and Audi S models lost, performance wise and dropped to be compared to more standard BMW models and where RS became more appropriate M competitor.
I believe BMW is trying to badge the models bit better for more appealing comparability with s models and consequently better sale outcomes.
2008 M3 coupe - DCT & EDC, AA