But there is growth. Perhaps it's the static percentage based graph that's misleading, I find this graph of more or less the same data rather intriguing:
http://farm4.static.flickr.com/3328/3421742213_db946c5ddf_o....
Your link is much easier to read.
However, that's not reflected in the visualization, and we're lead to believe that this is sampled with even steps over time.
Since the market has grown basically linearly, the arcs may actually be in direct proportion to the actual number of users, in which case there is very real growth.
The confusion comes when you see growth of absolute terms when the more interesting statistic is what the relative growth is.
Particularly, if one browser's arc remained the same size on each ring you might assume that it is staying the same. It has the same number of users, but it is losing prominence.
1) Because the perimeter of a circle grows as a function of the radius, an arc must grow just to represent the same share. This is misleading, giving an impression of growth where there is none.
2) It is difficult to tell which arcs on one side of the circle go with arcs on other parts of the circle. There is simply too much distance between them to judge accurately which arcs belong to the same time period.