Quite simply because I've never once been bitten by them -- with the exception of some haxies not working.
>I'm old enough to remember when Apple's OS was mostly rock-solid.
When was that? Because I remember Mac OS (pre X) beeing anything but rock-solid. I also remember the first X release being a disaster, and people moaning about issues I've never encountered in my (heavy) Mac use for every new release.
(I also remember the hardware problems, from the overheating cube and the G3 logic boards that died by the ton to the G5 tower leaking cooling goo).
First, because a lot of those bugs you only find in real-life bizarro setups, and beta testers are not enough. Besides not all beta testers actually help with bug reports -- some programmers just test their own software, others just want to play with the latest OS, etc.
Second, because not all of those bugs will be fixed even if a beta tester finds them. There will be a cost-benefit (opportunity cost) analysis, and some might need extensive changes to some subsystems, and only get fixed with the X.2 or even X.4 or X.5 release, half a year or more later.
Third, because there will always be bugs, and at some point you need to release.
Fourth, because OS releases usually also enable or leverage several new hardware features in Macs and iOS devices. Delaying the OS would mean delaying those hardware units, or putting them out with the old OS and no way to use some new advanced hardware stuff they are advertised with (stuff like Bluetooth 4 back in the day, Retina support, or something similar).
What OS are you talking about? OS X has always had buggy .0 releases. If anything it's gotten better over time, though I still agree with waiting for a .1 or .2.
If you mean Mac OS or earlier, then I wouldn't know. I was young and we always just kept whatever came on the computer.
My point about the .1 and .2 releases were that they're buggy, too. I look into my crystal ball and predict that 10.11.1 and 10.11.2 will both have serious issues (though not as much as 10.11.0. You really have to wait for the waves of bugfix releases after a point release to end before it's safe for human consumption.
Spotlight: Invisible files limitation; Processor usage and performance problems
DHCP Problems: AirPort networking dropouts, D-Link router problems, more
AirPort: No auto-reconnect after sleep; Connections dropping when switching from one base station to another Freezes during shutdown or startup, fixes
Widgets: Possible security exploit; Excessive memory usage; more
Check for bad login/startup items
CD/DVD burning problems: Errors, blank discs not recognized, more
Classic: Problems starting, more
Printer problems: Deleting, then re-adding
Font issues: "Fuzzy" type, more
SCSI Issues: Fix for Adaptec cards; Drives causing startup/shut down problems, more
Problems caused by QuickTime codecs
"Beeping" or "Chirping" noise back for some G5s
Bonjour issue and fix
Removable media devices not mounting, fixes
SMB connection problems, solutions
Wake-from-sleep issues
Speakable Items fails; workaround
Keychain import issue and fix
Safari 2.0: Problematic plug-ins, more
iPhoto 5.0.x: Unwanted image changes; Freezes on launch, fix
iSync 2.0: Deleted data; Problems synchronizing phones, iPods
Mail.app 2.0: Plug-in problems, removing bad bundles; Import problems; more
iChat AV 3.0: Performance issues
iTunes: Play does not continue during fast user switching, more
(...)
http://www.cnet.com/news/special-report-troubleshooting-mac-...