Nikolai - Russia is not a member of the European Common Aviation Area, EUROCONTROL or the EU, and as such an airline like Ryanair would find it *very* difficult to gain regulatory permission to fly to Russia from anywhere other than Ireland. It is possible that there may also be further bilateral treaties limiting Ireland-Russia traffic. This is why many residents of St Petersburg travel to Tampere in Finland to fly with Ryanair, and also why Lappeenranta airport in Finland near the Russian border has been suggested as an airport for a LCC.
While not a member of the above organisations, Morocco signed a separate deal with the EU liberalising EU-Morocco air traffic in 2006. The Russian Govt has not expressed a desire to do anything similiar.
I imagine also that the Russian Govt in any negotiations will want to ensure that Russian airlines like Aeroflot and Transaero continue to have a strong presence flying to/from the EU and do not suddenly find themselves drastically undercut on too many routes by a non-Russian airline.
Regular scheduled Ryanair flights to Moscow are not about to happen