I've never met Dennis but I've talked to him on the phone a bit, and exchanged a pile of email over the years, all about various Unix topics. Though I was nobody, he was always polite, always patient, always willing to pass on knowledge. I'm quite grateful to him for taking the time to exchange ideas and polish them.
bwk is the same way. We were working on extending awk to be, well, different (we made awk scripts be part of awk, so any statement could be a script and it could pipe to another script). I talked bwk about the idea and asked if I could do on top of his awk and the next day a tarball showed up of ~bwk/awk, had the source, all the regressions, the source the awk book, everything.
I love these guys, they did a lot of things I admire.