Windows: It can come with crapware pre-installed, such as "personal firewalls" and "antivirus" software which are mainly ad delivery platforms for the partners of whoever sold you the hardware. It can require you to go to malware-ridden sites with deliberately deceptive webpage designs in order to download some kinds of software. It occasionally requires maintenance in the form of digging through sometimes deliberately obfuscatory registry settings. It only runs Windows software; if you try to run Mac or Linux software on it, people laugh at you like you're insane. That's ready.
Linux: It must have no deficiencies. It has a package manager which performs dependency tracking (something alien to Windows, as far as I know) and contains no malware. It can never requires maintenance of any kind. It must run Windows software flawlessly. Only then will it be ready.
MacOS X: It has settings you can't change. It does things its way. If you disagree, you're wrong. It runs nobody else's software. That's ready.