Yes it would be useful in identifying what applications will not work when upgrading to Lion, but as you pointed out, any user can open System profiler, go to Applications and see for themselves.
The majority of the complaints I see is that there are Intel applications that the developer hasn't made fully Lion compatible (i.e it works but with issues). Developers had the previews to test out compatibility; the least they could do is post whether an update is coming or not would certainly ease the aggravation of upgrading then finding out a certain application doesn't work and not knowing when an update would be available.
I agree with what you've said, but then again, it's possible you and I KNEW, after reading online, to check the System Profiler and see those applications that definitely would not run under Lion.
While the checker wouldn't have uncovered Intel apps that aren't Lion-ready, at least those using Quicken or Mac Office 2004 would have known before installing Lion those apps would no longer run. (Those two apps seem to account for a good majority of the "....my app doesn't work anymore...." complaints.
Yes, the developers should have been more proactive...but Apple can't control what they do (or don't do!).
I think a pre-install compatibility checker (as MS did with W7) would have been an excellent idea. It would have stopped the vast majority of the thousands of 'my Office/Quicken won't work any more' threads.
The vast majority of users wouldn't know how or want to go to System Profiler. Good grief, they don't even know what a PowerPC app is - most of them anyway - and why should they.
There is a testing application from the German magazine "Macwelt". The tool is German, too, but rather straightforward to use.
Get the current version here: http://www.macwelt.de/fileserver/idgwpmw/files/1406.zip
It shows hardware compliance:
And lists incompatible Apps (PPC):
I agree with a previous post.....
Folks using a Mac because "....it just works..." wouldn't know some of their apps won't run in Lion. Was there any kind of notice to this effect when they started downloading it? I'd venture a guess that the majority of the population thinks Rosetta is a language-learning program, not a technology Apple used to run PPC apps.
It might have, but that's assuming anyone paid attention to it. Based on postings here, I sincerely doubt those reporting problems would have noticed. And if they did, they'd be screaming because they had to pay for and download Lion before they found out.
You just can't please some people, no matter what you do.