TC,
It's just a by the year account of things Star Wars-related as they happened. That includes not only the film releases but also the toy releases, comic tie-ins, novels, video games, etc.
I generally don't like those books because they go into too much detail on general minutae and don't concentrate on more important things. They're emphasizing the stuff that's not important at the expense of events that were a lot more important. Plus, regardless of what happens during a generic year, not much usually happens in the off-years.
For instance, between 1986 and 1992 not much happened Star Wars-wise other than wide releases of the VHS tapes. There were no new action figures, playsets, etc. and Star Wars merchandising was allowed to dry out. Sort of like the 7-year release cycle Disney used to maintain for its most profitable animated features. You don't wear out and bore the audience by keeping things constantly and allow for a new audience to develop in the mean time.
Since 1992, we've been constantly bombarded by one piece of Star Wars memorabilia or toy after another... Do you honestly think that all those years are that memorable and worth having an entry for?
They've done this kind of book for DC Comics, and frankly it's the same deal. There are a couple years of intense activity that are worth noting, and then you usually have 5-10 years where nothing worthwhile really happens.
I just don't feel like I need a book to tell me that!
I'd buy an art collection book, pre-production/production design book, or behind the scenes making of book that's a bit less pricy and not a coffee table book so that's heavy that I have to start heavy weight-lifting.
That's just me -- other people go for everything including these year-by-year books.