I've explained this in the past elsewhere on this forum. When people like Ryanair started quoting ticket prices without taxes, the legacy carriers had to follow suit. In addition, with fuel surcharges, these are extra and are listed as such (I believe systems like Galileo, Sabre etc don't have provision for any other items other than misc charges, where all that is lumped into).
On older ticket printers that still print out the old paper-style tickets, you will notice that taxes (departure, airport, arrival, whatever) are listed separately per sector, and the websites pretty much do that too.
It's all about looking competitive, especially when people like Ryanair start going off with "we're 90% cheaper than BA!" (as an example). Sometimes Ryanair is most expensive than BA would be, all because of their additional fees and charges.
S.