I just did a test and the Intel OS X package also runs on my iMac G5 PPC.
Does this mean the package is Universal Binary? and is this function going to be around for awhile!!
Officially, we support 10.5+ for desktop, but we do build a universal binary. Also, I'm pretty sure our WebKit build won't work in 10.4 or earlier. That said, we don't have any immediate plans to change how we build OS X binaries.