Update: MarkL, apparently a Google employee, in the comments writes:

And as for version 0.1 vs. 1.0... If enough people like the API as is, we are done. What we are really trying to do here is get feedback from you on what you do and don’t like. This is a real beta program where we want to hear what you have to say and where we will address as many issues with the design and interface that we can.

On the missing button when you don’t include the Google CSS, MarkL writes:

If you look REALLY closely, you will notice that the search control’s images are all done using image replacement. So that “button” is really a background image on an adjecent div. Why? So that when you plunk this into your site, if you don’t want that button, its a simple css override to use one of your own buttons. All of the graphic elements, color scheme, etc. are done this way so that with a very small amount of skill, this think can look right for you, your site, and your visitors.