BART-CD 2.0 uses a MS Window XP embedded to boot a system (this is the reason you starts with the Windows XP bootup screen), so if you have a problem booting a specific machine (usually a modern machine) I think that you have a problem with some XP driver that you need to boot the machine and that driver is not included in the XP of the BART-CD.
"... but that seems pretty silly when 2.0 was sold as a bootable recovery disk." BART-CD is a bootable recovery disk with some limits (MS Windows XP limits).
What happen if you made a DOS bootable diskette and boot a machine with NTFS file system in his HD? Can you read the HD? So a DOS diskette, that a lot of us use for several years, isn't a bootable disk because I cannot read a NTFS file system?
BART-CD 3.0 uses Windows PE 2.1 (built from Vista SP1) and all the drivers included on Vista SP1 are present, so all new drivers and devices must be included.