3.7 GB (that’s the size of the download) are still a lot and keeping the size of downloads as small as possible is certainly a valid goal.
I think Apple shaved off about one GB or so compared to what they pressed on DVDs and that’s certainly noticeable for many people. My parents’ house (in Germany) has this really awful DSL connection, more than 4,000 kbit/s are just not possible. Having to download 1 GB less would save them over thirty minutes. (Downloading merely 3.7 GB would take them over two hours.)
Making stuff only few people use optional is still a great idea when you want people to download it. Not everyone has FIOS.