I agree that if you play the game you should buy the book. But the issue is that you dont really need the PhB to play 5E. Only spell casters in my group really use it in play. If you play a fighter you only really need to check the PhB when you level up.
This is definitely true. I'd say for 5E you only need one copy of the PHB for the table.
I have long been a loud and obnoxious supporter of these books. Me and my buddy pooled our resources and bought god-knows-how-many 3.5 books. The stack was taller than a toddler.
I will say this: For the past 3 years I've been living abroad and in areas where these books are not easily accessible. I've been playing with friends through Roll20 and the like. I would love to have real copies, but right now, living in China, I'd pay a horrible price, would have to use someone else's card to order it, and then trust in the Chinese postal service to have it get to my apartment (which has been about a 50-50 shot for me). Of course, PDFs are my best options - Pirated or otherwise.
The only significant thing I've noticed switching from real book to PDF is that I am way more likely to flip around in PDFs. I read the 4E (hardcover) handbook cover to cover when I borrowed it from a friend. I
never even played 4E! When we started 5E (in PDFs), I skipped around a lot, looking at my favorite classes, spells here, equipment there, and only settled into reading it in detail when I agreed to DM.
Because I put less attention and effort into it, I'm way more likely to make mistakes and mis-remember stuff from PDFs. I still remember obscure rules from Mouseguard, but have to reference the PHB on what Frightened means in 5E all the time.
Maybe it's age, but I prefer to blame it on not having the book in print in front of me.