It's another manifestation of ryr's inability to raise the "headline" fare, as to do so would drive customers into the arms of the the opposition that provide better service (i.e. pretty much everyone else). So the money must be raised somewhere else.
The "average fare" may well be lower than a few years ago, but the average cash handed over by the punter has scarcely changed. However, ryr has worked out well that the public stupidly don't seem the consider all the add-ons as part of the fare. When people start waking up to this, it'll be very bad for ryanair.
Ryanair are not low fares, they are low one part of the fare and good at advertising.