I guess the point of this article is to show that you can uses these alternatives in addition to the system default, but you don't have to. I don't see any item of these better than what it is replacing (CrashPlan vs Time Machine, any one? And Preview is the fastest PDF viewer I have ever used). You cannot say this for many other platforms. Hell, there is not even any built-in KeyChain or Time Machine counterpart in many systems.

I took a quick look at the list, and found myself only using a TextEdit replacement (MacVim) and a QuickTime replacement (VLC). Even these two are not really replacements but more like complements.

A Mac is the only machine that I can start hacking after installing one application - MacVim. Even easy_install is built in.