My thoughts exactly. I'm regularly using bootable cd's, as USB bootable device compatibility is an issue for a lot of systems. These bootable discs need regular updating: new versions of recovery tools, virus definifition files, bugs in the multiple bootable environments on it, etc. It would be a rather expensive task to write a new disc for every minor change, and the readability of rewritable media is far from optimal.Not to start a slanging match, but that statement is inherently wrong. You are not even considering the fact that not all computers can boot from USB drives, and therefore multisession boot CDs like Puppy Linux are still very essential.
your argument for pupply linux falls down cos you can run it from flash memory
On the topic of multisession discs, there are very useful when making incremental backups, so you don't need to waste discs unnecessarily.
Furthermore, I think incremental backups alone would justify the implementation of multisession writing: one should be able to make backups at any time, not just when there's enough data to fill up an entire disc. When it comes to that, it might already be too late... In addition, the absence of multisession writing would make one to use a less reliable rewritable medium for crucial backups.