I guess we Mac users are so cash-flush, we're just itching to give some away.
The site, Retina Mac Apps, is a good 'un. Thank you.
It's not really comparable to Linux packages. GPL software is nice, but it's usually also a lot of work until it works the way you want - paid apps are there to do that for you. You could still install most Linux tools using Macports / Homebrew. At some point you will recognize that sometimes spending 20-30$ instead of investing hours of your time is worth it.
Now concerning Apple's own software: IF they fit your needs they are usually a total no-brainer. Pages/Numbers/Keynote give you 90% of the power of MS Office, in a more consistent way and at 1/4 of the price. Similar things can be said about Aperture and Final Cut X, Logic Pro even being the industry leader from what I hear. Apple certainly doesn't make a profit on those alone.
I think it can partly be attributed to the higher-end software dev/design teams being first to the punch with Retina, and partly because most of these apps are productivity / media apps. Aperture, Coda, etc. are definitely worth the price of admission – they're fantastic software.