Anyone knows ? I mean persons, not just 'Valve".

I think it's fair to say that the maps are now a teamwork process. I can't be entirely sure, but more then one person work on a given map. Like the church in Avalanche is made of Props more then anything. So i guess this was made by a modeler to be inserted into the map.

Because they are so complex now, to make great maps you almost need many person now. Even myself, I am thinking of teaming up with other ppl in the future to create new maps.

I think the future of maps lie in teamwork a bit like mods need programmer, art artist, level designer, mappers, modelers etc..

A dev dod member can of course answer this question better. It's just the way I feel from all that I have read.

The maps were a teamwork process before as well.

I'm not sure about the mapping but I believe IR textured most of Donner and Anzio and some other stuff for Flash and Avalanche.