Canada: the Liberals chicken out

As expected, Canada's Liberal Party has chickened out, and will be supporting the Covervative Party's budget. They're demanding conditions - quarterly reports on the effects of the budget's stimulus package on the economy - but these are so weak as to be no real concession at all. Which begs the question: if the Liberals are just going to support whatever the Conservatives do in government, why are they pretending to be an alternative?