Difficulty is increased because of added new mining devices.
As I know - mining devices now are produced and shipped in big quantity only by BFL.
Last 4 increases all were around 30% (29.4% - 32.22%). This coincidence (almost same percentage increase 4 times in a row) never happened before.

Does it mean that BFL specially ships devices not in their full potential, but in specially calculated quantities to keep this 30% increase ratio?
And, possibly, all who are now still waiting for their BFL device - could have them delivered month ago if only BFL would ship all at their full potential?