Perjury is a criminal matter, which means that the full range of investigatory powers available to the police come into play. They seized a computer from TS's house. If, theoretically, they found e-mails relating to the type of life-style that the press had alleged he enjoyed, it could contribute to the case against him and others. (Such evidence would not have been available to the defendants in the civil case).
As I perceive it, a lot of the lies which are put forward in a criminal court are ignored because the defendant is found guilty anyway. (i.e. the CPS seek to prove the defendant guilty. Once they've achieved their goal, they regard it as 'case closed').
The situation where a person sues for defamation (and commits perjury to do so) is very different. The plaintiff hasn't been dragged before the courts by the police and CPS. He's made a positive decision to use the court process to fraudulently get money from the defendants. The courts take fraud seriously, so it's hardly surprising that they take it extremely seriously when fraud is committed by actually using the processes of the courts (which, allegedly, is effectively what TS did)
Chris