But there is this research into problem resolution for German Ebay customers
http://www.psmag.com/culture/were-sorry-not-all-apologies-ar...
that indicates that a real apology from a vendor is more effective than (some amount of) cash in getting a customer to withdraw negative evaluations.
This is, incidentally, also the rationale behind never talking to the police: unlike aggrieved customers, police more or less are professional assholes. It's not their fault per se, and it's not a slur on police officers, but even more than lawyers, police are more or less constrained by the adversarial nature of the criminal justice system to be total assholes almost all the time. Actually, this asshole theory seems to explain a lot about the legal system, for instance why divorcing couples seem to be total assholes to each other as soon as they both lawyer up.
Your point is that most people aren't assholes, and can be reasoned with. Fair enough! But there are assholes, and eventually you get bit by them, which is how big companies develop lawyerly antibodies to them. As for politicians, they're all lawyers already, and it's practically their job to be assholes to each other, and if they slip up there are plenty of assholes in the press to make up for it so appealing to the people's better nature is automatically more difficult.
I can't imagine that there are actual liability issues here; it's more than Dell (incorrectly, I suspect) thinks that using weasel words looks better than saying "oops, we're horribly thoughtless and incompetent".
Historically, I'd agree, but my observation (and opinion) is that real time mass communications and an ever dropping attention span mean that half-hearted apologies (or even sincere ones!) merely fan the flames, whereas radio silence lets the storm clouds pass because people's attention spans are so short.