Google sure is great at technology, but I think they're not nearly as great at doing business as Apple or Amazon are.
Cloud computing is all about creating a good blend of technology and business. If you don't get the business off the ground, you won't have the stamina to seriously invest in the technology, particularly in terms of building lean, scalable operations. Building scalable systems is perhaps 1% inspiration (distributed algorithms), and 99% transpiration (cost-effective operations). If you don't get it right, you'll be looking at this big red number below the line and will have to kill it. The fact that Google is already huge does not matter that much, it's not being big that's hard, it's growing fast and staying afloat.
Indeed, Amazon is an Internet shop. They'll sell anything to anyone, anywhere, and they do so for ridiculously low margins. That's a mighty competitor to be up against. Google on the other hand has never been very successful outside of advertising, and have only been a high margin business.
Not saying that Google won't be successful in this space. If they're willing to lose money on it they could achieve a sizeable market share comparable to Microsoft's. They lack Microsoft's gigantic sales network, but make up for in developer goodwill. However, catching up with the lean operations machine of Amazon seems infeasible at this point. What they could do is focus on their core strengths and open up their massive data sets and tools for all to use. So far they have been very reluctant to do so however, afraid to harm their core business.