Because you never know what trivial bit of information may ultimately prove to be vitally important.
Some the captchas are hard to read. I usually need to reload them at least a couple of times to get a word pair that I can actually read. But I'm not sure an audio version would be a good replacement.
Yes! I have had a horrible time with the captchas on blogger lately and as you said they are impossible. Glad to hear it's not just me!