[psyklic]

I'd guess that tipping is mostly a socio-cultural thing -- it is expected; it would be considered rude not to. In addition, peer pressure is a factor -- unfortunately, I doubt that I would tip as high as I do or as often as I do if I didn't have other guests at my table.

Online, you just don't feel bad if you don't tip -- there is no peer pressure and no expectation. So, of course it doesn't work out.