Valleygirl, don't hesitate to put an idea out there! That's why we post here--to get other's input, ideas, & to discuss things. And, most importantly, learn something new! 
Please bear with me if I am a bit too detailed or bird-brained; I just want to relay the information as accurately as I can, as I comprehend it! (And, please, anyone feel free to add or correct this, so many can learn something new!)
I tried to research what you had read, & this is the best I figured out:
Under the classification system for all animals, all birds are the Class 'Aves.' Next, we have the Order. The Order, 'Passeriformes,' often referred to as perching birds, includes many of our common backyard birds. Then, we have the Family, 'Emberizidae,' which includes some species of buntings, brush-finches, longspurs, sparrows, towhees, all juncos, etc.. (The brush-finches in this family are not in North America but Central & South America, unlike the finches we know; the house, Cassin's, & purple finch are in the family 'Carpodacus.' ) Perhaps this is where a bit of confusion may arrive. Where the debate occurs is in the next classification steps, Genus & Genera, most specifically, the Genera.
Basically, the all Juncos are in the family 'Emberizidae.' In Sibley's Guide, they are arranged by families, & are listed in the 'Emberizadae' family, as they should be. I think he is staying with what is known & undisputed, by grouping the birds by family. As well, most of us learning to identify birds
can appreciate them being grouped this way, with common names.
I thank you all, in advance, for your input! No matter how insignificant, or controversial you may think it is, it really helps people who have 1 thing in common-- love of birds!
Valleygirl, by the way, I did get a fantastic buy on the Sibley's guide. I will say that if you live in the good ole USA, for $11.35, it is a fabulous bargain! This is the link to go to, & you must sign up for google checkout, which gives you the $10 off. You do not have to ever use it again, but it is free to use!
http://www.buy.com/prod/national-audubon-society-sibley-guide-to-birds-field-identification/q/loc/106/30635076.html
This is the buy.com link, but if you look in the right hand column, you will see a place called a-1 books, with a sell price of $21.35. With your $10 off, it will end up being $11.35. Now, the only thing to keep in mind is that I think they ship USPS media mail, so it takes a couple days longer, but at $11.35 for a $35 book, (even though I was dying with anticipation,) who can really complain?!
I will add, just in case, that I am only a consumer; I don't personally know a-1 books; just ordered from them off of buy.com, which I am an occasional (happy) customer! If anyone experiences any trouble with the ordering process, just message me & I will do my best to help out.
Finally, anyone who has this guide, the Eastern/Western edition, or any other guide they use, please let me know about them! I want a small handful, & I need direction with good ones to own; otherwise, I'll just check the others out from my library! Thanks!
"So many sparrows, so little time!"