I must admit that I didn't come upon the answer myself, but the novel did stimulate much thought and discussion, and finally, illumination.
I'd recommend this novel, but only if you'll allow the authors to tell the story. Much like Gene Wolfe, if you insist on interpreting this story yourself you'll miss it.
And here's the clue: the Difference Engine is the main character.
My favorite little bit of the book -- and I think the fact that this IS my favorite bit will demonstrate what kind of person will like this book -- is when John Keats shows up as a clacker. GOD, that was brillant! First, you have to get who Keats was (not nearly enough people know him as one of the most brilliant poets ever), know his desire for literary immortality, about his early death... but you also have to understand the mutable nature of people's professions, of people who were "before their time"... in the world of TDE, Byron, Shelley and Keats never become the "Big 3" of the 19th century, but a Prime Minister, a dissident, and a graphic designer, respectively. People who dismiss this book without knowledge of the artists of the 19th century are missing a big point. Here we finf Sterling's "computers change humanity" points... Prime Minister in our world (Disreili) writes crappy books, while the greatest of the Romantic poets become hackers....
Secondly, I agree that you need to have an actual knowledge base in early computing to get it all... that Ada Byron's program was a strange loop NEEDS to be understood, because that leads towards...
... wait for it...
THE PLOT! Yes, there IS TOO a plot! Gibson/Sterling's quotation that it should/might take 50 years to understand the ending is because it won't be for at least 50 years that OUR computers achive what the Difference Engines did in the alternate 1990's of TDE -- to wit, true artificial intelligence, which has only its beginnings in the computation serieses of our own century.