I also noticed that some of these distros don't have websites anymore.

Having all the tools handing in One dvd is very useful indeed, no need to locate, compile, test, or waste time trying to find the tool/exploit/document, for one thing if you are doing penetration then BT3 would be handy, however for Forensic analysis where you do not want to pollute the swap/disk helix would be more suitable, and so on. One thing i have against these dvds is that the software will be out of date, and vulnerable soon enough, and runing them or using them as superadmin/root in a networked environment calls for problems, i rather see images for USBs, and how to make them is not that difficult any more, there are bootloaders that can you help you achieve this, and there are distros that allow you to customize and add modules easily BT, Fedora, Knoppiex almost all live CDS allow customizations these days.

I agree. I have a few CDs I keep in my pentesting kit (mostly because I haven't had the time to try to make my own distro, yet), but it seems like a good solution, rather than one DVD with everything.

Also, what if you are doing forensics on one computer and pentesting (or whatever) on another computer? Then you need two discs, anyways.

That's my preferred method. Also not every machine you come across can boot from DVD, even if you take this route might be handy to have a couple of CDs just in case