Very true. While you may know about strings, integers, floats, and arrays, it's always good to read about them in the context of a new language you're learning. The Well Grounded Rubyist is riddled with useful tidbits. The predecessor to that book was Ruby for Rails (also by David Black). Each time I read the book, I picked up new information, even the third time around.
When we learn, we learn by applying new material to what we already know. Hence foundations and context. When you read, especially something like a book on programming, you're not going to absorb it all. Also, programming books shouldn't be treated as one and done reading. Each time you read, I guarantee something will pop out based on previously acquired knowledge.