Former editor from K-12 publishing here: That's correct (although Georgia and Florida also have sizable pulls). Both California and Texas have large populations and have official, state-wide adoptions, which of course means there are huge amounts of sales to be made all at once. If you live in a so-called "open territory" state, chances are good you're going to get the version made from Texas or California, depending on where they are in their adoption cycles and when you try to buy. There's generally a layer over top the "main" files that holds all the Texas state icons and state flags and BBQ icons and whatever else that get plastered all over the page to appeal to that market, and the layer is simply removed for other states. And given Texas's ideas on "education," that's not a good thing. (Don't get too smug, California. Your state standards can be just as bizarre and arbitrary.) There was a lot of hope in not only the publishing industry but education as a whole that the national Common Core standards would help limit the power of those two states in deciding curriculum, and make it possible for a kid who moves from one state to another to not get smacked down due to completely different requirements in different states for the SAME grade level, but it's already a rough road, and Texas was the first out of the gate with their "HUR DUR STATES RIGHTS!" argument and didn't adopt the Common Core. They also routinely have some of the lowest test scores (particularly in math) in the union, but I guess they know best, right?
Fun fact: I once worked out a spreadsheet to show the overlap between as many official lists of state standards in math as I could, with the idea of thinking about a new program based on that, but there was so little overlap just in my eight-state sample that the project was scrapped.