Who says they aren't? Surely you don't think that dev seeds are their only source of testing. I'm sure they have vast labs full of diverse hardware exactly for this purpose. If I were them, I would measure the defect rate and only push things to dev seeds when I'm likely to only learn something that I don't already know.
No I don't think they are developer testing is the only testing. I do think though that it is the sole form of software diversity testing that they do.
I think the internal testing tests how well apple software runs on apple software. That would nice if all customers wanted to do was run apple software 95% of the time. They don't.
I seriously do not think that Apple has a regression suite to run Microsoft Office through its paces on a significant portion of its code base.
There are multiple directions they bugs could come from. As far as running as a broad diverse set of hardware, yes, Apple probably has all but the very largest software shops beat on coverage. However, I don't think that Apple has the developer population beat on the diversity of idiomatic use of the APIs that the OS and hardware provides. Catching bugs in one of the dimensions doe not mean you are catching bugs in the other.
Lol, no...what I'm talking about is software engineering.
Software engineering would be testing something significantly before you ship it. Holding back PowerPC software from being tested doesn't accomplish that. Yes they may be testing one dimension of the software internally before going more widespread. However, at some point would have to add the others far enough before shipping to be useful.
On a side-note...people keep using the word 'beta'...is that the official designation of these "seeds", or are we all playing fast-and-loose with the language, here? If it's the latter, then it would probably be best to not make assertions based on the connotations of the word.
Defacto these are the beta. Beta is a state of software that can (pragmatically should) very through some release labels. Beta a significant property of beta is about who gets access to the software so that can get feedback on quality, not a specific release point.
Seeds are release labels/points.
These might be labeled as alpha if Apple commonly did more a more widespread release to a more general population before release. They don't. The only expansion in the testing population beyond apple is to the developers for the Mac OS X release for long while now.
They could also be labeled as Alpha if folks think there is some hidden secret sauce that Apple is going to introduce at WWDC. The new "and more thing" about the interface that is hidden right now. That is a bit wishy-washy from a OS API perspective. Does any thing API is going to spring some new API that isn't currently present at WWDC?
If you want to heap the Finder and other GUI do-dads into the technical OS present it isn't a Beta.