Familiarity? Not speaking for anyone else in this regard I shall relate a short story.

When starting my first tech support job, I knew vaguely TCP/IP, some systemV type shell and that I was jumping into the deep end into boiling water. Before starting I had asked one of my similarly geeky (but more successful) school friends what I could do to get up to speed, what are some more valuable skills to have. Two words and a gesture were all he gave me, 'Learn perl' pointing to a tatty copy of the o'reilly 'perl in a nutshell'. This is in fact the only paper perl reference I have ever owned, buying new edition on occasion. Why do I keep buying the same one ? Familiarity. - that book saved my stressed out backside more time and frustration that I can express. It was good advice then and I have clung to it.

As you say, this is not the forum for a trees vs electrons debate. I use both to the extent that I LOVE having a solid reference on my desk, books smell good (!?) , I've never come across a coffee ring on a perldoc -f page, but can reminisce about almost every abused corner and tear of each of my copies of 'perl in a nutshell'. The perlers who can't believe you don't have a copy of the Camel may have similar quirky feelings about that book - but who am I to speculate.