I'm not looking to over categorize, but lets face it where do most people go for help with an MCU, oh yea a dedicated forum. I do use AVR freaks and when i was using PIC I went to the pic forums.
So I think it stands to reason to broadly categorize uC's based on manufacturer as this is the main automatic classification as their assembly languages will be different, the tools will be different and they all have their own architecture particularities.
Not many people are familiar with so many uC's so if they come on here with a view to help people they have to rumage around to find topics they can help with instead of pulling up the section they are knowledgeable in.
Hopefully it would encourage more use of the section, at the moment it's an amateurish mess in my opinion.