I don't think there is really any consensus on this standard to be honest. Most search engines don't index no-follow links per se, but they do follow them for crawling. Even Google, who first proposed the nofollow, sometimes actually do follow according to some tests linked in the wikipedia article. The results show that if the link is already in the index (eg has been followed elsewhere) then it does get followed and indexed.
The nofollow is really just a keyword to point out that the link isn't being endorsed by the author - It's more a content guideline than a strict order for robots to obey. So I disagree that you're breaking standards or creating a robot that's not well behaved by ignoring it.
I would have liked to have done a bit more with this so that I could have respected nofollows, but injected the URL as a brand new seed URL but other commitments took over and I never got around to it. Since the ideal nofollow behaviour is somewhere between ignoring them and not ignoring them I figured the option to ignore them was a good start and submitted the patch, but I'm not precious about it.