There are something like 30 models that run the new OS and hundreds, no, thousands of applications, browser extensions, etc!
It is impossible that they will have tested all of it, if they did, it would never come out!
Besides, if you want to see a scary OS launch look at how MS does it. Releasing beta software at high prices to hapless customers who get to be the beta testers.
How is it 30 different models? Consider that SL supports only Intel macs.
Moreover the applications, browser extensions, etc should not come into picture because people are having issues with the OS (expose laggy) on a FRESH install.
Even I expect Apple to release a really stable OS from day 1 since they control both HW and SW. Microsoft's task of getting their OS to work on ANY computer (thousands of potential configurations) is much much more difficult.