What a pointless discussion
Messenger and Tech Talk are in the same category simply because they fit together nicely and don't fit in any other categories. Maybe you could call it "Technology" or something if we're being pedantic.
With thought to the addition of new forums, the fact is, the current forum setup doesn't have any over-burdened forums but doesn't restrict conversation because of the lack of a relevant forum. I certainly don't think there's any point in adding forums just because they fit in a certain category arrangement, if nobody will use them much. Like... what's with the suggestion of a Bug Reports forum for messenger?
If there is to be a forum addition may i suggest a current affairs-type forum? such forums exist on other sites and they work quite well. i reckon that would start some interesting conversations at least...