Well, I can't speak for CS:GO, but Dota 2 just lends itself really well to the model Valve has taken. Heroes are unique with distinct styles, and their models are generally large enough that you can actually notice the cosmetics. It's also not a historic game, so there's more freedom to create interesting stuff. There are also uniquie game elements that lend themselves very well to cosmetics, such as wards and couriers.
The problem with selling maps is the CoH2 community is just too small. People won't buy maps unless they're reasonable certain that they will be able to play on them. When there's barely enough people automatching to find a game in a timely manner, maps that segment the community aren't going to be successful.
Honestly, I think if Relic had gone the cosmetics approach to DLC right off the bat, everyone would be a lot happier. Make interesting skins, give units custom animations or voice lines for certain skins, sell customized faceplates and base buildings so players can pimp their clans, let people sell custom HUDs. Hell, I'd buy a custom HUD if it fixed the terrible default CoH2 HUD, and I'd buy some cool-looking skins if they were worth the money and came with some cool extras. No way in hell will I buy a commander though. Not going to support a business model that's fucking a game that already has enough problems of its own.
Sigh... Inverse you remind me of so many other ways Relic could have made $$, but alas, they went with commanders. I would totally buy custom "real" skins for my units, get more unit dialogue, cool custom faceplates, etc... When I first started playing LoL I said, "man ill never buy anything". Then I realized I got some much enjoyment out of the game I figured I'd give back, so I bought numerous skins for my favorite champs.
Oh the possibilities if Relic/Sega just looked around them!