Actually, it was Mac OS X 10.4.6 that came out last week, not 10.4.5.
Yes, patches and minor 10.4.x updates are free, either by manual download or by running the Software Update utility. They're kind of like Service Packs in the Windows world.
However, the big complaint is the frequency of major updates. The last "must have" update was 10.2 in the summer of 2002. Only 14 months later, Apple came out with 10.3, which was faster and looked a little nicer, better encryption, little tweaks and additions, and added the really awesome (IMHO) Expose feature. It was a worthwhile upgrade for me, $79 as a student from the online Apple store and $99 for my parents via Amazon.com. Only 18 months after that, came 10.4 which really didn't give me a whole lot more for my money. Yeah, 100 more features, 90 of which I don't use. And now, this summer, only 14 months after 10.4 came out, Apple will be releasing a developer preview of 10.5, which will probably be in customer hands only 18 months after 10.4 originally shipped.
Many shareware/freeware Mac applications require 10.4, which has caused a forced upgrade for many users. Most commercial Mac applications now require 10.3, which means most Mac users who use brand new software have to be using a version of their OS that's less than 3 years old. This is annoying to people who are used to using, for example, Photoshop CS2 on Windows 2000, new software on an OS that's 6 years old.
Yes, 10.3.x updates all the way to 10.3.9 were free... and my current 10.4.6 update was free... but I'm going to have to pay for 10.5 unless I buy a new Mac that has 10.5 preinstalled.