Lots of fans seriously over rate their players. Sunderland fans were valuing their keeper at 15 million before he went the RS.
The reason nobody has bought Fellaini for this supposed release clause fee is because people from other clubs don't think he is worth it, and I'd have to agree, I'd be sick if we spent over 20 million on Fellaini.
His 'release clause' isn't half unique as well. Fancy setting a specific date, two years in advance, half way through a contract and half way through a transfer window for a release clause to suddenly become invalid.