I wouldn't call the book outdated. What was written, even in the first edition, are still perfectly good methods and techniques to use and will make great beer. What has changed is that we have found new additional ways to do things - not necessarily better, it just gives us more options. Plus we have access to much better equipment (which may help some folks)
As someone who was brewing back then, I don't think the yeast are any better now than they were back them. What is different is they are packaged more conveniently and we have access to more strains. I don't think there is much quality difference.
What has changed is that the homebrewer of today is often MUCH better at managing the temperature of fermentation. Back then it was pretty much pitch the yeast and that was it. The beer fermented at whatever temperature the room was at - often on the warm side. We didn't ahve an appreciation for how a couple of degrees can affect the beer. Under these conditions, the yeast are more likely to have an impact on the flavor, hence the advice to move the beer to a secondary to minimize the influence of the yeast cake on the flavors. Now that many of us are much better at managing the temperatures, we have found that it is OK to leave the beer on the yeast longer with much less influence of the yeast cake on the flavor. However, if one does not have a good control of temperature, then racking to a secondary is still very good advice, unless you like the extra flavors from sitting on the yeast longer.