I could argue that it seems today that there is a reduction of genres, and an increase blanding to the lowest common denominator, a mashing of things in the name of storytelling. It has increasely become more of interactive fiction and adventures, with increased dexerity elements, or adventure being mashed with action, and things dumbed down to pulling levers in certain order or hunting the key card. Action has assimilated adventure, outside of Indie stuff, and then you now see RPG also being assimilated. The stat building element of RPGs has been getting into about everything at this point.
So, you come out with large scaled budget blanding of genres, that are supposed to appeal to everyone, in the name of adventure.
imho you're blaming the wrong culprit. It's not in the name of adventure more than it is in the name of mass-appeal.
Also, everything should come in its good dose. If all games were like King's Quest, we'd never have Zelda. Also, adventure doesn't nessecarily mean dumbed down. Zelda OoT is rift with adventure, yet is was not dumbed down. I think balance in all things is key and it's not because some games were dumbed down to fit a lucrative formula that gamers should be on a witchhunt for games that seek adventure as a nutrition for gamers.