I think this has more to do with the euro/dollar exchange rate than the supply/demand for aircraft.
So yes, with the exchange rate, Ryanair are getting less euros for their sold planes, but they are also paying less euros for their delivered planes.
2 points
(a) I believe they are hedged for the new purchases, so x-rate movements won't affect them for the cost
(b) Ryanair is a big arbitrage trader on aircraft prices - the missing €40m from 2008 to 2009 prices is a big hit (for which the employees will ultimately pay)...