Well, super simple is relative! The project cost 250,000 USD to the developers; it might not be a lot, but for most indie developers it is an impossible sum to have to back your project. The interesting part, though, is that I think they used a system not too different from Moai to develop their game, using C++ with Lua scripting on top.
Also the artwork, it is deceptively simple. The awesome Craig Adams actually researched painstakingly for years before he found his unique style; the amazing thing about pixel art is that it looks simple, but to get to have your own style and expressiveness, it takes a lot of research and artistic skills and practice. If you look at the animation sheets of the game, you can see that characters have literally hundreds of animation frames! Then the dialogues (which is the part I liked less in the game) are very sophisticated and written to appeal a certain audience and some marketing requirements (limit of 140 characters, for example).
What I want to say is that however you look at it, S&S is not a simple game by any means. It is a very complex, expensive for indie standards, very self-conscious, and always a smart game.
What I want to say is that Tim, Ron, and their team can obviously look at S&S as an example of a modern successful adventure game, but they do not need it for what concerns the actual gameplay. The games they have worked on in the past are in my opinion richer, more fun, and even more innovative than the pure adventure game part of S&S.
Do not get me wrong: I loved the atmosphere of S&S, I loved the art, some of the music, the sound effects; it is a game that must be praised because it was a bold effort of creating beauty in a market filled with crap or downright evil game design. It is a great interactive/multimedia experience. But the storyline, the puzzle structure/dependency chart, interactivity, and dialogues cannot compare to what we had in games like MI 1 & 2, Grim Fandango, and so on - in my opinion, of course.