That was the whole thing about PCs - if my memory of Cringley's "Triumph of the Nerds" serves, the genesis of this category was IBM rushing to a market where other "closed" vendors such as Apple were already established. It wasn't that PCs were open "by design" but more that they did things quickly and gathered other vendors "off the shelf" notably Microsoft and Intel, and had a copyrighted "BIOS" holding the whole thing together. Once Compaq reverse engineered this BIOS (through some legally clean techniques) the market was blown open to the clone manufacturers and Intel and MS were happy to play along since at the end of the day they were just shipping more units .... probably couldn't do it these days due to DMCA and other modern copyright legislation in other jurisdictions.