[morzh]

As long as the device gets used regularly (not left in storage for 10 years) coupling electrolytic caps are almost immortal as they do not see any real currents going through them and their temp is always at the ambient.
Obviously if not used they develop typical leak that could only be cured by reforming but with those it is not worth it as they are mere pennies in prices. If not replaced they screw up the DC biasing of the transistors they couple into which though probably won't burn anything will get distortion to increase.

Electrolytics are used there probably due to the fact that they cost very little and film caps could cost you many times that.

Let's take 1uF / 50V caps.

For example, this aluminum cap is $0.09 apiece. (the cheapest of its kind in Mouser)
http://www.mouser.com/ProductDetail/Lelo...aLVWvPk%3d

But this film cap is $0.63 apiece (also cheapest of its kind, same voltage / capacitance)
http://www.mouser.com/ProductDetail/Arco...dYmxyHI%3d


Now imagine you are in the business of building consumer electronics and you need an inter-stage cap in quantities of a few hundreds of thousands to millions.
Or (in some very mass-produced devices) - tens of millions and up.