I got summoner as part of the nordic in and out pack, i decided to check its page. only to not find it.
it does not show up in the store when searching for the game, checking for games by nordic shows only 3 game when i have purchased about 20 of them
and clicking on the review button on the library goes to
http://www.gog.com/game/summoner#reviews=1
which gives a 404 error.

Well, it was called "in and out" for a reason - all these games were removed from GOG, so you can't check their pages anymore (only via https://archive.org/index.php). You can however still download them.

is this a joke? why would they do this?

No, it's not a joke.
35 Nordic games were removed 1st time on September 1 - see this "Last chance promo" with 2 important posts
http://www.gog.com/forum/general/last_chance_special/post226
http://www.gog.com/forum/general/last_chance_special/post729

Then they came back, but just for 4 days in "Nordic In-N-Out" promo.