I think you've fallen for the marketing trap where a list of features has to be present for it to be worth something. Not many lists include code and platform optimizations because it doesn't market well. I've used OS X since 10.1 and each update has gotten remarkably better. Things have mellowed out in 10.5 but the OS feels fully baked.
In the end I don't think there really is anything they can do to make me pay more money for the OS. I already bought iWork 08, I bought SuperDuper! for backup, and everything else I use is either open source or comes included with the machine. If Apple wants me to upgrade, then they need to discontinue security updates for 10.4 or some widget I badly need needs to be 10.5+. And honestly, it's not me that Apple has to contend with, it's my wife and her iron grip over the budget ;)
It could be if you were required by some regulation to use a UNIX certified OS. IIRC, there were little feature changes that warranted the certification.
As for myself, I have an older iMac that won't run SL, a netbook that runs Linux and I am perfectly happy with both.
I'm hoping that a scorched-earth fresh install of 10.6 will either eliminate the amazing flakyness or alternatively point me to a hardware problem.
I also wouldn't trust Tiger security on an external network.
And I preferred spotlight in 10.4. In fact, 10.4 was all around a much better OS than 10.5, which was the first update to Mac OS X that felt like a step backwards.
Of course, I'll be updating to 10.6 as soon as I can get my hands on it. If nothing else, the promise of a 10.5 that doesn't suck is worth it. To be fair, 10.5 is much better now then when it shipped. When it shipped, it was terrible.
(a) intentionally, knowingly fixed
(b) disclosed.
Still on Tiger here too, which is my main reason for wondering if I can get away with the $29 version!?
Edit: Mac Box Set seems a better choice too, US link: http://store.apple.com/us/product/MACBOX-101801 169$