On statistic I read(I don't remember the source) is that less than 30% of dental restorations performed in the US last year used amalgams. So even many the dentists who still use amalgams try to use other substances when the patient is willing to go for it.

As for as amalgams being unnecessary, my dentist said that once every month or two he still uses amalgam, as composite fillings are not suitable for a large cavity in a molar, or perhaps a bicuspid. The choice would then be an inlay or onlay, or a crown. Some people who don't have dental insurance aren't willing to pay the much higher cost for an inlay or onlay, and choose an amalgam instead. Some dentists might place a composite filling where it is not appropriate(ie. a large cavity in a rear tooth). This might not last so long, or might be quite likely to allow decay to form under the filling.