Thank you Steven for posting this update
Indeed it is very surprising that Toro Rosso decided to replace both Buemi and Alguersuari particularly that in recent days both were confident of their chances.
Having said that, Toro Rosso have always been saying that their line up would be two of those four drivers. Ricciardo did well at HRT and Vergne impressed during the young driver test. It will be a good fight between those two especially that one of them could move to Red Bull in 2013.
There are only a few seats left for Alguersuari and Buemi to try and grab for 2012. A Williams seat is still available while the driver lineup at Force India has yet to be announced although it is almost certain that it will be two from Sutil, di Resta and Hulkenberg. There is also a seat available at HRT and while Caterham have confirmed their lineup, there is speculation that Trulli's seat may be in doubt
Check out the
2012 driver lineup page for the latest information