The Blob taxonomy idea helps to avoid collisions, too.

If some developer needs to support CAB files on an aggressive project
schedule, he can guess at an unused archive file type number, and be
reasonably sure that someone else working on an urgent schedule for an MP3
isn't going to grab the same number.

So the developer can both continue to work toward their deadline, while they
wait for someone from ISC to say, "yes, you can use 543 as a Blob subtype
for CAB, and it should be standard in the next official build of InterBase
6.0.2.93".

In other words, what's missing from Jim's scheme is a central authority for
designating new Blob subtype ids on a very quick turnaround.

Bill Karwin