At the time of the initial report, I suspected that a reason Google seemed so angry was that the hackers had tried to inject new vulnerabilities into Google software that would then damage third-party Google users (either via browser compromises of downloads of Google-distributed client software, like Desktop/Toolbar/Chrome/etc.).

Stealing 'secret algorithms' is in one category of transgression. It's still somewhat flattering to the target. It's driven by curiosity, not always a bad thing. To the extent such theft-of-secrets enables competitors to increase market share by improving their own operations, it hurts the target, yes, but might still be net-beneficial to society in a dynamic long-term analysis. It's theft, but not really violence. A victim will adopt countermeasures, and might expect compensation/damages, but may not be moved to retaliate in-kind. A rational weighing of costs and benefits tends to dominate the choice of responses.

On the other hand, to try to corrupt a company's offerings to damage their customers -- and possibly destroy the company's reputation as a trusted source of downloadable software -- moves into another more serious category. It's malicious and destructive. The victim may feel existentially threatened, and feel obligated to retaliate using any means available. A rational weighing of options may not matter; there is a urge to punish, even incurring large costs in the process.

Google's initial response made me think they viewed the China breaches in the latter category, despite the limited details.