E-TTL is not all it's cracked out to be

E-TTL is the technology that fires ultra-brief flashes imperceptible to the human eye and measures and adjusts light output from a strobe to make it "just right" for the subject, distance and ambient light. It is, in effect, the "auto" mode for the flash.

What I found from a few brief and completely unscientific experiments is that when using my Canon 430EX flash on-camera in E-TTL mode the shots come out consistently overxposed outdoors and underexposed indoors.

There are threads in Canon and Strobist forums explaining why it is so. The universal agreement seems to be that indoors the FEC in E-TTL mode should be set to +1.

My question is: if all photographers know that, why doesn't Canon?

Source: Experience, photography-on-the.net, Strobist on flickr