I think it's definitely true that writing styles have changed. There's a strong feeling nowadays that you MUST hook the reader in the first chapter -- if not the first sentence -- whereas a lot of older books really expect you to hang in and stick with it.
You'll see this in movies, too, I think. A lot of older movies just sort of expect you to hang in there until the good bits. I recall "The In-laws" extremely fondly, but when I watched it again a year or so ago, I was shocked at how long it takes for the interesting and funny bits to get rolling. There's a lllllloooooonnnnnggggg set-up for the jokes and you're just expected to behave yourself and wait for it.
I think any technique -- writing or movie making -- refines and changes over time. In these cases, I think the techniques has changed at least in part due to the many competing sources for attention. The reader is going to read A book, but unless you hook them immediately, it may not be YOUR book.
