As a buyer of English translated manga, I noticed that there was, at one point, a big break in the manga that TokyoPop released. I know I wasn't the only one to notice. I found out why a while back on the lj for ShutterBox (it belongs to the artist herself!).
I quote (from
here):
Speaking of ShutterBox~ we've been told by our editor, Rob Tokar, that because of the new association TokyoPop has with Harper/Collins, books must be schedule for publication one full year in advance. So, looks like ShutterBox 4 won't be out until Sept 2007 this year. -___-***
That looks like the reason for the break in time between all TokyoPop volumes. That is the best explantion I have heard. It's the publisher's fault!
I want my ShutterBox!