DP,
Increased descent speeds generally mean increased fuel burn. Econ descent speed in an FMC is partially dictated by Cost Index.
CI= Fuel Cost/Direct operating cost
So, as fuel prices have risen, the CI has generally fallen. The lower the CI entered into an FMC, the lower economical speeds it produces (basis being fuel cost saving becomes more important than airframe time cost saving).
On an individual flight, the cost saving is not huge. Multilply that by a fleet on each sector across a flying season though and the cost saving can be quite substantial.
Companies review this with variable quality of course, but the savings are defiantely there at the moment - high oil price=lower speed (up to a point for aerodynamic reasons.....)
Some people just like flying fasy (macho thing?, think they are doing the company a favour?). Those who descend fast in the days of high fuel costs may feel they are doing great service, but in the true cost analysis, are doing their employers little good. I'm not suggesting any of these are necessarily the case with the airlines you mention, but suggesting some pilots have this mentality.
In many cases it might well be a case of companies not providing the right, and accurate, information for crews to use. Some have fuel cells, which regularly review costs and revise CI's accordingly. Some may not keep on top of such issues and hence don't provide the crews with education and accurate information on such areas.....
30W