Why do I need Linux when all the best open source programs have easy-to-install Windows binaries?
Good point. However, don't forget the downside of this system - software updates are a pain with each vendor adding their own software update daemon that nags you about updates. Or (for better or worse) no update system at all. Mac users have the same problem but it's not as bad because typically almost all their applications come from the same vendor - the same vendor that makes their OS.
The software repository system is part of the reason Linux distributions (Debian, in particular) have a reputation for better security.
I agree that Linux could use some more stability - and I think the LTS releases from Ubuntu are a good step in the right direction. Simply enable the "backports" software channel in these releases and you'll get fairly up-to-date versions of all the big name applications while keeping the core something stable that proprietary software vendors can target.