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It's pretty common for a software house to buy up the competition to kill it through attrition.

So, err, what competition did Carrara/Eovia present to DAZ, exactly? I'll save you the trouble: none.

Carrara does make some sense from the perspective of having a platform to move D|S figures into and out of, as it provides some fairly decent modeling, a very nice render setup, and other goodies. 

I know that DAZ bought Bryce to save it (and the still-sizeable Bryce user base) from the oblivion of Corel's software graveyard, where the one other bit of unaccounted-for MetaCreations software (Canoma) sits.