I never played mother-may-I when I was young, but as I understand the game it's all about favouritism.
I don't think so. I believe "Mother may I?" refers to the sometimes high-handed authority wielded by early-edition DMs. Mostly this happened because DMs had to fill in a lot more blanks than in recent editions. When combined with an antagonistic attitude, this lead to a situation where the PCs could do virtually nothing without the DM's express permission. It is seen as part of the bad half of "DM empowerment". People who experienced particularly atrocious incidents of it are likely to not have fond memories of early editions.
As D&D evolved, starting in 3e and culminating in 4e. Players and PCs were given increasingly defined capabilities. So, for instance, its possible in 4e for a combat to resolve without a player ever asking the DM "can I do X?" or "can I reach Y with this spell?" I know because I've DM'ed several that way. This is highly unlikely to occur in older editions, both because of "Theatre of the Mind" issues
and because doing something fancy like...pushing an enemy back with your attack
required the DM to adjudicate how that happened.
This looseness or incompleteness in the rules is why there are such varied experiences with older editions. Some people felt that fighter only got to say "I attack", while others felt that they did all sorts of cool things...and the truth is both are right, because it was campaign/DM dependent. (Although, I must say, despite all the griping around here about how weak and boring and horrible fighters were before 4e came and rescued them from obscurity...I
never had trouble finding people to play fighters or their close kin.)
Now, 4e did offer a solution to the "Mother May I?" DM smothering the players' creativity. However, that cure seems to have been worse than the disease. Given some of the things my local 4e haters have said, this was a big part of why 4e "didn't feel like D&D" for them. Additionally, by defining every PCs abilities so rigidly, they also rather rigidly defined playstyle. I know that this is a spot of some contention, so I'll just say that I, personally, had a lot of trouble adapting 4e to fit a less "gonzo magic" playstyle.
How this will play out in 5e is rather up in the air, of course. Personally, I think they just need to focus on better DMing advice and guidelines. Early editions tended to have an attitude that lead to DMs cackling from behind the screen at the exquisite tortures they had devised for the players. While this may have been a misinterpretation of "Gygaxian" play...I don't think its an irrational one. (see "Horrors, Tomb of") If they can more clearly define the DMs role as less of an adversary, and more of a...Director, writer, co-creator...whatever, this would go a long way, IMHO.