First of all, i think that Apple will only continue to support the Macs which can run Panther. This is Apple's way of 1) cutting back on the support for all the various Macs they make; and 2) thus, this is their way of phasing some computers out of their OS support.
Second, i think that they should have Tiger on DVD and CD. My G4 will run Tiger, but my beefed up G3 will not unless finding a work around installer. Besides i don't think that Apple will not support those people that don't have a specific ROM drive. I mean didn't Apple have a DVD and CD-ROM disc versions for iLife?
Correction--
System Requirements
Macintosh computer with a PowerPC G3, G4, or G5 processor
-600MHz G3 or faster required for GarageBand; G4 or G5 required for GarageBand software instruments
256MB of physical RAM
Display with at least 1024-by-768-pixel resolution
Mac OS X v10.2.6 or later (v10.2.8 or later recommended)
QuickTime 6.4 or later (QuickTime 6.5 included)
4.3GB of disk space required to install GarageBand, iTunes, iPhoto, iMovie, and iDVD; or 250MB to install iTunes, iPhoto, and iMovie only
Important Notes:
DVD drive required to install GarageBand and iDVD
iDVD requires a 733MHz PowerPC G4 or faster.
Burning DVDs using iDVD requires an Apple SuperDrive.
Burning iPhoto archives to CD or DVD requires Mac OS X v10.2.8 or later.
I think that this must allow users of computers with out the dvd-rom to install certian software packages, iDVD, and GarageBand are the only programs which require a DVD drive. For those of you that have iLife, did they ship a DVD disk and CDROM too?