numbskull has it about right, but Keg, I'd be careful about recommending wikki-pedia as it has been known to be rather less than accurate and is often rather subjective. i.e It's not validated nor policed, no matter what the owners say. (bit like here)
Simple reason = Share buyback = surplus/eexcess cash on B/S , Cash in Hand (i.e. already on B/S) is at optimum, so how do you best use the excess cash ? (as numbskull says, debt is currently cheaper than dividends, but not for long the way the libs cooked things up)
Reduce the issued #, increase the capitilisation ratio (Total cap Value of Company divided by the number of issued shares, which = share price, look at the smh.com_dot_au to plot the effect of this , easy you can download this into an excel sheet and watch the effect) , and a nice side effect is that each of the remaining/residual shares increases in price.
neat , eh ?
wonder who thought of it........................
???
Oh , and silly me for not considering this also, the "action"of a share buyback is normally triggered by something, which is what WOD actually asked, and now that I've managed read your question properly.
Only reason for a share-buyback (aside from what numbskull said - i.e excess cash) is that it will be better used than the strike/market rate you'd get for putting that cash in an at-call/money market short term account, that and it increases the equity/resistance of QF external hostile intents, either that or they are planning to consolidate their position for something as yet un-announced.