1) there is no viable search competitor to Google, therefore
2) search must be a much harder problem that takes more engineers than we expect, therefore
3) it's hard to reproduce Google's success because you can't actually do what 10^n engineers do in a weekend.
I think that's plausible, but it needs to be emphasized that search could very well be not that hard, but no one has overtaken Google because they have inferior marketing, distribution, present too high of a switching cost, etc.
Just because Google has a bunch of engineers solving that problem (and reproducing what Google does seems complex for correct reasons pointed out in the article) doesn't mean that the engineers are actually adding that much marginal value. My guess is that even if Google invested less in search engineering, and didn't solve real time indexing and some other edge cases this well, it would still be leading the field.