I assumed rd=disk1s2 and boot-uuid=xxx referes to the same thing, the partition being booted, but rd is not absolute (will change if you shuffle disks or remove partitions) and boot-uuid is absolute (will never change unless you reformat the partition).
I think the problem in chameleon is that is adapted to booting from EFI and does not take into account other situations like booting from MBR.
The docs says: "The boot: prompt waits for you to type advanced startup options. If you don't type anything, the computer continues starting up normally. It
uses the kernel and configuration files on the startup device, which it also uses as the root device."
Using linux terms as an analogy:
startup device - boot partition - /boot/grub - /Extra/Extensions
root device - system partition - /(root) - /System/Library/*
If you have chameleon installed to EFI System Partition, system partition is always different, but in a typical MBR installation chameleon's boot and root partition are the same, but if you have snow leo and leopard, depending what you select to boot they could be the same and different.

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AsRock P45TS | C2D E8200 | GeForce 8600GTS
Mac OS X Snow Leopard 10.6.1 + Windows 7 Ultimate 6.1.7600 + Fedora 11