If Boeing give Ryanair a spectacularly good deal then Stansted has also done the same since the mid 90's, until recently when they are now being charged an appropriate rate. The "grounding" of aircraft has nothing to do with BAA charges.
Stansted will prosper without further Ryanair expansion - signs are there, Eos, Maxjet both expanding and AA starting this winter with 2 x daily from March 08. Long haul is what Stansted's been crying out for and it now appears to be happening.