I used a Mac for a few years a while back (and still would if they had some lower end versions of their PowerMacs with Core 2 Duo instead of Xeons), and installing applications was just as easy as on Windows. More importantly, however, it was MUCH easier to keep track of and get rid of applications after they had been installed.
BSD-style ports and RPMs and Debian packages are fine too, and also quite a lot easier to manage than Windows applications. It’s a bit annoying that libraries and applications are treated as equals, since that makes it more difficult to see what you’ve actually chosen to install rather than having dragged in as dependencies, but it’s possible some improvements have been made in this regard in the Linux world since I last looked at it.
As others have pointed out, the lack of a standard way to install things on Windows complicates everything a whole lot. The average user’s “Program Files” is a mess after a year or two. Yes, it can be avoided, if you’re very disciplined, but in practice that’s just not the case for the vast majority of computer users.
I’m not even sure who to blame - Microsoft actually tried to solve this, since there is “Add or Remove Programs” in the Control Panel. But there’s a lot of applications installed that are not listed there, so it didn’t quite work out.