2012 - Mountain Lion: http://www.webpronews.com/mountain-lion-may-be-hurting-your-...
2011 - Lion: http://forums.macrumors.com/showthread.php?t=1194978
2010 - Snow Leopard: http://reviews.cnet.com/8301-13727_7-10426564-263.html
I'm not saying Apple is perfect, but when you've got millions of people downloading an OS - many of which are jumping 2-3 entire major OS versions - even 0.01% of people having the same problem is going to result in hundreds of people with that problem. When you combine that with a public discussion forum run by the company (that's regularly indexed by the major search engines) and a small but vocal portion of the customer base that feels entitled to immaculately perfectly functioning devices because "they bought an Apple computer" (read: luxury) and you end up with runaway threads of coincidence-now-fault.
"Wow, Apple is giving away 10.9 for free? Even for old machines running 10.6? Gee, I've got a 5+ year old laptop with the original battery I haven't used in a while - wonder how it'll work with that."
Saw that someone mentioned the MacBook Air Gen 1 (they probably meant Gen 2 since Gen 1 had 32-bit EFI and maxed out at running OS X 10.7) - which originally came out with 10.5 ... but you could still get 10.9 onto it if you did the USB installer trick. In point of fact - Apple actually added the visual indicators for servicing your battery in 10.6. If people are installing 10.9 over the top of 10.5 (it works if your machine can run 10.9), they will likely be seeing a battery warning indicator for their 5-6 year old machine that has been a valid issue for quite some time (especially since the battery isn't considered user serviceable on a Unibody Mac) - it just never popped up in their face. I would be more believing of this thread if every single person posted their battery readings and all turned out to have amazing low cycles combined with amazingly reduced capacity (which is when the Service Battery dialog appears).
If you find yourself to be in the same boat as the people in this thread, you should probably read this KB article from Apple and immediately have your laptop retrain its battery knowledge:
http://support.apple.com/kb/HT3964
"Intel-based Macs: Resetting the System Management Controller (SMC)"
After performing normal troubleshooting, these symptoms may indicate that an SMC reset may be necessary:
-Power-: [...] The battery does not appear to be charging properly. [...]"
After calibrating it did indeed determine that, yes, you still had a failing battery.
I'm not quite in the same boat as you - my machine is a MacBook Pro 2008 pre-Unibody. But I've been through the "Service Battery" warning on this 5 year old machine before. And they were right! Chemically, the battery had degraded and could barely hold a charge for more than 25 minutes. The machine would power off randomly without the 10 minute "charge me now!" warning because the power curve was so bad, it could never predict I only had 30 seconds left.
Apple goes to great lengths to try to educate their consumers about how to protect the life of the batteries of their laptops:
http://www.apple.com/batteries/notebooks.html - Long term storage tips, maintenance tips, best practices, a little calendar reminder you can add to iCal to remind you to do these things, etc.
http://support.apple.com/kb/HT1446 - What you can do to increase your battery life, how to diagnose battery problems, etc.
10.9 itself! http://support.apple.com/kb/HT5873 - Click on the battery icon. It will tell you what processes are running right now that demand high power. The Activity Monitor has a new "Energy" tab showing per-process power utilization. At the bottom are various charts and statistics about your battery usage.
People abuse the hell out of laptop batteries by leaving the laptop connected to the charger all day, every day, like it was a desktop. They're perpetually 99%+ charged which stresses out the battery. The battery is meant to be used - use it!
And like you, I'm not experiencing the issues in this thread under 10.9.
Maybe I'm just lucky. I had to replace my wife's macbook pro battery a month ago, same age as mine. Her's swelled up though, and was preventing the trackpad from clicking.
How do you figure?
This is more because one of Apple's slogans for OS X is "It just works.", not "it just works, but only on most hardware".
I agree, it's unreasonable to expect everything ever to run smoothly, but this is the expectation you set when you are brazen enough to market your gear as "it just works".