fund managers getting greedy here??

check out this graph

STW is an index fund, similar to the Vangard fund and is supposed to track the ASX 200
Well in the first half of the decade the share price seems to have tracked the index, then in the second half it seems to have diverged. the share price appears to under perform the index.

I looked at the financials on comsec and bookvalue is recorded for the first three or so and then they stop recording it.

Any ideas why this divergence in price and index might have occurred.
Could it have something to do with management fees? Could it be a case of fund managers getting greedy?