I would actually argue that making a good search engine with quality and responsiveness worldwide rivaling Google web search turns out to be an architecturally hard problem.

A basic web crawler is not. A semantic web crawler and associated search engine capable of mapping real human input to useful information and dealing with the heterogeneous structure of data on the web, with low millisecond latency?

Bing has been working on that problem for years now, how come they haven't caught up more with Google?