It's easy to criticize a policy like this, but they do have millions of clients and it does work. I'd rather have a clean interface for my google then a creative one. Actually, i'd like more clean interfaces all around. There's no shortage of creativity in web design, but large applications/sites with so many users are not the place to test it.
Clean and creative aren't mutually exclusive though. It's perhaps too obvious an example, but Apple's design is on the whole pretty clean - and to my eyes at least looks like a lot more care was given to it. One of my main problem's with Google's design isn't how plain it is, it's just that it looks half finished at times - it doesn't need more, but it doesn't look like it was well thought out.
This could very well be intentional.
Take speaking a foreign language as an example:
1) If you're a novice, a native can tell right off the bat and cuts you some serious slack.
2) Even if you speak their language at an intermediate level, a native can still tell it's not your first tongue and, depending on your demeanor, cuts you some slack.
3) You speak their language fluently and can be considered by any native speaker to have mastered their tongue. However, when you (confidently) mess up in the slightest, you can very well look quite retarded to the natives.
In Google's case, that half-finished look could be very intentional and can look a bit humble, as in "I'm sorry I haven't had time to clean up the place, but please come in and make yourself feel at home".
You can feel a bit better knowing you don't have to be constantly alert as you would around the presence of perceived perfection.