I suspect this also, but believe it can't. Too many photographers and non-pro users still on G5 towers and iMacs to justify Apple sacrificing a hefty slice of their user base to competition like Adobe Lightroom if LR3 continues to cater to that segment when it's released. It simply wouldn't make good business sense to go "10.6 or higher required" with Aperture 3 unless Adobe also abandons PPC as well.
At the time of their releases, Lightroom 2 still supported G4s, and Aperture 2 still supported G4 Powerbooks for this reason I believe. Time has moved on a bit, so I expect at least they'll now drop G4 support and raise the cut-off to 1.9GHz G5s, like they've done with iMovie.
On a side-note, my local Apple retailer still uses G5 iMacs on their counters to run their business. I find it very ironic that they can't upgrade their business systems to 10.6 without chucking their otherwise perfectly good Macs. It's things like this (ie, the cost to businesses, including Apple's own) that lead me to believe they will at least continue support for older Macs with their applications if not with the OS itself. For a little while at least anyway.
I was in your shoes too. I had told myself that Apple was going to update Final Cut Studio and Logic Studio before Snow Leopard hit. NAMM passed ...no Logic Studio update...then Musikmesse...then NAB with no Final Cut Studio update. Now we're almost halfway through June ..WWDC is over and we have no Aperture or Final Cut Studio or Logic Studio updates. Then the true gravity of Apple's words hit me.
"Snow Leopard lays the foundation for future advancements in OS X" . A first blush it's another marketing quip but Apple's actions clearly show they PPC and Carbon trains have ended. The future is 64-bit Cocoa.
Are there plenty of PPC users out there using Apple apps? Sure but these computers are now 4 years old at a minimum from their launch dates. They are "end of cycle" and under most circumstance ready for a refresh.
Let us also be honest about these three verticals.
Final Cut Studio - video editing and production is cool but in the overall scheme of a multi billion dollar computing industry it's a niche
Logic Studio - also a niche for audio production
Aperture- photography ...niche.
I'll be honest and say what Apple won't say. If you have a PPC computer it's time to upgrade. We're not going to slow our evolution of OS X for people who's computers are by most part in need of refreshing and depreciated.
It doesn't really matter what Lightroom does, that's beyond Apple's sphere of influence. What matters is that Apple can leverage the unique benefits of Snow Leopard to great effect. I expect all of the Apple Pro apps to be delivered for Snow Leopard and they will perform with so much more speed and polish the only people who dogmatically stick to their PPC will be non Professionals. If you make money with your computer "time = money" and a faster Aperture means more work gets done. If that means a new spanking multi core Mac then that's what it means.
Here's what PPC users are asking Apple to do.
If they deliver Leopard Intel and PPC version of the next apps then here's what Apple faces.
They will have no less than 4 build to QA.
Leopard PPC
Leopard Intel
Snow Leopard 32-bit
Snow Leopard 64-bit
Folks ...logic should be taking over now. Anyone who remotely knows software development knows QA testing on 4 different builds is asking for trouble.
If Apple gets rid of PPC then there's no reason to do Leopard Intel (because every Intel Mac can run Snow Leopard) and thus you have the most logical solution being that Apple simply supports Snow Leopard. The logic is undeniable.
