People used to pay money for Trumpet Winsock, then a TCP/IP stack became critical infrastructure, and you no longer paid for it. Web Browsers used to have a commercial model (Netscape), then the Web become so critical, it became commodity infrastructure. Disk compression and encryption? Table stakes. Video decompression/compression? I could go on and on, but ALOT of functionality that used to be commercial add-ons has become commodity, and required OS infra. It's just paid for, and no on charges.

Otherwise, hey, let's unbundle Mobile Safari, and Mail, and Maps, and when you buy an iPhone, the first thing you have to do is buy all the builtin default apps.