Apparently Purslow included the clauses as a way of persuading Torres and Reina to stay on last summer.
This was from Tony Barrett of The Times on Jan 8th:
One of Purslow’s many mistakes was belatedly put right today but there are still countless others still to be rectified as Fenway Sports Group, Liverpool’s owners, are discovering to their cost since their takeover in October. Chief among them are the release clauses that Purslow inserted in the contracts of Pepe Reina and Fernando Torres which will allow the star duo to leave this summer should rival clubs match the conditions written into in their current deals.
It has been suggested by Purslow’s allies, a steadily dwindling group at Anfield, that the clauses were inserted to protect the club. Such logic bears no scrutiny, not when the decisive manner that Arsenal dealt with serious interest in Cesc Fabregas following the World Cup. “Not for sale at any price” was Arsenal’s reaction to interest in their best player from Barcelona. No fee was suggested, no price placed on his head and no weakness shown. Liverpool, by contrast, watered down the contracts of two of their best players to such an extent that it would be no surprise if both left this summer. That is Purslow’s legacy and it is one that FSG are now struggling to deal with. The time bomb is ticking and they are yet to find a way of defusing it.
At least they have now found the fuse, though. Removing Hodgson from a post that he should never have been offered in the first place is a crucial step in the right direction. It sends out a message that mediocrity will no longer be tolerated and it gives hope to players and supporters alike that the club’s owners are willing and able to make the big decisions that Liverpool have cowered away from for far too long as a result of endemic dysfunctionality in the boardroom.