Apologies in advance if it is a stupid question, but do...

Apologies in advance if it is a stupid question, but do underwriters usually have a get out clause in the agreement if the index were to drop below a certain level? I noted in the retail offer docs (or mulch based on current share price) that if the ASX200 drops 15% below the close on 14 August 2009 for 2 days or more they can walk away.

Any thoughts?