The existence of the Basic D&D PDF makes the buy-in for 5e very flexible, with a whole spectrum of price points, since even the core rulebooks don't really need each other to function.
An experienced player or savvy consumer can download the Basic D&D PDF for free.
A new player can but the Starter Set, and if he wants more, download the Basic D&D PDF. The Starter Set's existence as a physical product makes it ideal for attracting new players, and its $20 price point places it firmly in impulse buy territory for a mom walking through Target looking for something cool for little Timmy.
Someone who is interested in trying 5e can pick up a 5e adventure off the shelf, read the back, see that everything needed to play is free online, and buy the adventure.
An experienced player could download the Basic D&D PDF, read it over, decide she likes it, and buy the Player's Handbook only, confident that she will be satisfied with the monsters and magic items in the Basic D&D Set, and won't need the DMG or MM.
A DM running a game for some friends could use the Basic D&D PDF, see that his players are perfectly satisfied with their player options, but decide that he wants more monsters. He buys the Monster Manual but not the Player's Handbook.
An experienced player could decide he wants the PHB and DMG, but is satisfied with the monsters in the Basic D&D PDF and his own homebrew.
And so forth. There's a buy-in price point for everyone, is what I'm saying, and it is very easy for anyone to ease into the system without paying a great deal at any one time.