Nodding while reading a lot of the previous answers.
I can only answer for our family, but I am also guessing that a lot of people, in the year or two years before starting officially homeschooling will buy some kind of preschool curriculum. I personally don't think it's necessary, but we have been using Sonlights preschool packages for the past two years--at age 3 and 4. Basically, they are wonderful literature collections that you read aloud do your child--and while the packages do include a few other items (games, scissors, some fun critical thinking workbooks) it has been a wonderfully informal learning experience for us.
I also wonder if families that intend to homeschool tend to be more aware of learning opportunities and/or purchase more play-based "school" items like pattern blocks, magnetic letters, chalkboards to scribble on, etc. during the preschool years. DS (5 now) learned to read about a year ago, but it was not due to any formal teaching on my part. Sure, we talked a lot about print and I answered his questions/pointed out features of print on road signs, etc, but much of it was his own curiosity leading to his discovery of how to read. Once he started writing, I did purchase a handwriting book for him--since as a former teacher I have seen a lot of kids who have developed bad habits with incorrect letter formation. We didn't have a set routine for "doing school" though--just kind of did a few pages when he felt like it. The read-alouds took more time, but I would have been doing that anyway, with or without a curriculum.
In short, even though "school" last year was extremely informal, DS picked up enough reading and math from it that a typical kindergarten curriculum probably would bore him to pieces this year. I wonder how common this experience is.
Just my two cents.