Similar to your "Reason b)", I've been suspecting a "conglomerate" of wealthy bitcoin players has come together and is trying to stabilize the price. I think it's been going on for longer than just since the bitcoinica problem, though. I also think the "target range" is being adjusted sometimes. It used to be "$5.0 +/- 0.20" and is now 5.00 to 5.20.
This is wild speculation, of course and this might be totally wrongThe only other explanation I can come up with for the astonishing stability since March would be a herd-effect with traders saying: "oh, ok, so it'll be around $5 now, so I'll just sell slighty above and buy slightly below". If enough money acts like that, it's self-fulfilling.
Of course the market cannot be manipulated in the long run (at least not against its general will: it might be possible to "stabilize" it into a certain trend and I would welcome that).
anyhow, thanks for the update, I think it's spot-on.
Yes, it is also correct that those stabilization efforts have been going on already before the bitcoinica disaster.
And also yes, it will fail for sure. The market does what it wants, not what a few players want.