Ask HN: Why is Ryanair monetizing airplane lavatories?

As I imagine most HN readers have already seen, Ryanair as announced a plan to charge passengers 1 Euro to use the bathroom on their planes, which has been met with near-universal derision. (See http://www.google.com/hostednews/afp/article/ALeqM5iZziXJPnwEjtWkoF4sD8vI8q2Wag for a typical article.)

My question is: why do you think they are going ahead with this?

Possible reasons:

a) an untapped source of income (seems doubtful)

b) to discourage bathroom use (the stated reason)

c) the free publicity from the news reports (i.e., there's no such thing as bad press)

d) an attempt to reinforce their positioning as the cut-rate/no-frills carrier

Anyone have any thoughts? Is this the collossally bad idea it appears to be, or is it actually a clever move?